497

September 26, 2012

Securities and Exchange Commission

Via EDGAR

Re:       Principal Funds, Inc.

File Nos. 033-59474, 811-07572

Interactive data files for previous 497 filing

Pursuant to Rule 497 under the Securities Act of 1933, as amended, Principal Funds, Inc. (“the Registrant”) is filing interactive data files that relate to the supplement the Registrant filed on September 14, 2012 (SEC Accession No. 0000898745-12-000610) and now is incorporating by reference.

Exhibit No.                                                                                     Exhibits

Ex-101.INS                                                        XBRL Instance Document

Ex-101.SCH                                                      XBRL Taxonomy Extension Schema Document

Ex-101.CAL                                                       XBRL Taxonomy Extension Calculations Linkbase Document

Ex-101.DEF                                                      XBRL Taxonomy Extension Definition Linkbase Document

Ex-101.LAB                                                       XBRL Taxonomy Extension Labels Linkbase Document

Ex-101.PRE                                                      XBRL Taxonomy Extension Presentation Linkbase Document

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

Equity Income Fund formerly Equity Income Fund I (Prospectus Summary): | Equity Income Fund formerly Equity Income Fund I

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

Equity Income Fund  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in dividend-paying equity securities. The Fund usually invests in equity securities of companies with large market capitalizations (those included in the S&P 500 Index, which as of December 31, 2011 ranged between $1.57 billion and $401.25 billion), but may also invest in equity securities of companies with medium market capitalizations (those included in the Russell Midcap ^® Index, which as of December 31, 2011 ranged between $117 million and $20.51 billion). The Fund invests in value equity securities, an investment strategy that emphasizes buying equity securities that appear to be undervalued. The Fund will also invest in real estate investment trusts and securities of foreign issuers.

Equity Income Fund formerly Equity Income Fund I | Class R-1 Shares

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PIEMX

Equity Income Fund formerly Equity Income Fund I | Class R-2 Shares

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PEINX

Equity Income Fund formerly Equity Income Fund I | Class R-3 Shares

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PEIOX

Equity Income Fund formerly Equity Income Fund I | Class R-4 Shares

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PEIPX

Equity Income Fund formerly Equity Income Fund I | Class R-5 Shares

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PEIQX

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

MidCap Value Fund I (Prospectus Summary): | MidCap Value Fund I

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

MidCap Value Fund I  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in a diversified portfolio of equity securities of companies with a medium market capitalization (those with market capitalizations similar to companies in the Russell Midcap ^® Value Index (as of December 31, 2011, the range was between approximately $117 million and $20.51 billion)) at the time of purchase. The Fund invests in value equity securities, an investment strategy that emphasizes buying equity securities that appear to be undervalued. The Fund will also invest in real estate investment trusts.

MidCap Value Fund I | R-2

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PABUX

MidCap Value Fund I | R-3

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PMPRX

MidCap Value Fund I | R-5

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PABVX

MidCap Value Fund I | R-4

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PABWX

MidCap Value Fund I | R-1

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PLASX

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

LargeCap Growth Fund I (Prospectus Summary): | LargeCap Growth Fund I

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

LargeCap Growth Fund I  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with large market capitalizations (those with market capitalization ranges similar to the companies in the Russell 1000 ^® Growth Index (as of December 31, 2011, this range was between approximately $117 million and $401.25 billion)) at the time of purchase. The Fund invests in growth equity securities; growth orientation emphasizes buying equity securities of companies whose potential for growth of capital and earnings is expected to be above average. The Fund may also invest in securities of foreign companies.

LargeCap Growth Fund I | R-1

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PCRSX

LargeCap Growth Fund I | R-2

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPUNX

LargeCap Growth Fund I | R-3

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPUMX

LargeCap Growth Fund I | R-5

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPUPX

LargeCap Growth Fund I | R-4

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPUSX

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

SmallCap Growth Fund II (Prospectus Summary): | SmallCap Growth Fund II

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

SmallCap Growth Fund II  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity

securities of companies with small market capitalizations (those with market capitalizations equal to or smaller than the greater of 1) $2.5 billion or 2) the highest market capitalization of the companies in the Russell 2000 ^® Growth Index (as of December 31, 2011, this range was between approximately $23 million and $3.7 billion)) at the time of purchase. The Fund invests in growth equity securities; growth orientation emphasizes buying equity securities of companies whose potential for growth of capital and earnings is expected to be above average.

SmallCap Growth Fund II | R-1

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPASX

SmallCap Growth Fund II | R-2

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPMNX

SmallCap Growth Fund II | R-3

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPMMX

SmallCap Growth Fund II | R-5

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPMPX

SmallCap Growth Fund II | R-4

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPMSX

XML

SmallCap Growth Fund II (Prospectus Summary): | SmallCap Growth Fund II

SmallCap Growth Fund II  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity

securities of companies with small market capitalizations (those with market capitalizations equal to or smaller than the greater of 1) $2.5 billion or 2) the highest market capitalization of the companies in the Russell 2000 ^® Growth Index (as of December 31, 2011, this range was between approximately $23 million and $3.7 billion)) at the time of purchase. The Fund invests in growth equity securities; growth orientation emphasizes buying equity securities of companies whose potential for growth of capital and earnings is expected to be above average.

XML

SmallCap Blend Fund (Prospectus Summary): | SmallCap Blend Fund

SmallCap Blend Fund  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with small market capitalizations (those with market capitalizations similar to companies in the Russell 2000 ^® Index (as of December 31, 2011, this range was between approximately $20 million and $3.7 billion)) at the time of purchase.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

SmallCap Blend Fund (Prospectus Summary): | SmallCap Blend Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

SmallCap Blend Fund  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with small market capitalizations (those with market capitalizations similar to companies in the Russell 2000 ^® Index (as of December 31, 2011, this range was between approximately $20 million and $3.7 billion)) at the time of purchase.

SmallCap Blend Fund | R-1

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PSABX

SmallCap Blend Fund | R-2

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PSBNX

SmallCap Blend Fund | R-3

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PSBMX

SmallCap Blend Fund | R-5

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PSBPX

SmallCap Blend Fund | R-4

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PSBSX

XML

LargeCap Growth Fund I (Prospectus Summary): | LargeCap Growth Fund I

LargeCap Growth Fund I  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with large market capitalizations (those with market capitalization ranges similar to the companies in the Russell 1000 ^® Growth Index (as of December 31, 2011, this range was between approximately $117 million and $401.25 billion)) at the time of purchase. The Fund invests in growth equity securities; growth orientation emphasizes buying equity securities of companies whose potential for growth of capital and earnings is expected to be above average. The Fund may also invest in securities of foreign companies.

XML

Equity Income Fund formerly Equity Income Fund I (Prospectus Summary): | Equity Income Fund formerly Equity Income Fund I

Equity Income Fund  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in dividend-paying equity securities. The Fund usually invests in equity securities of companies with large market capitalizations (those included in the S&P 500 Index, which as of December 31, 2011 ranged between $1.57 billion and $401.25 billion), but may also invest in equity securities of companies with medium market capitalizations (those included in the Russell Midcap ^® Index, which as of December 31, 2011 ranged between $117 million and $20.51 billion). The Fund invests in value equity securities, an investment strategy that emphasizes buying equity securities that appear to be undervalued. The Fund will also invest in real estate investment trusts and securities of foreign issuers.

XML

LargeCap Growth Fund (Prospectus Summary): | LargeCap Growth Fund

LargeCap Growth Fund  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with large market capitalizations (those with market capitalizations similar to companies in the Russell 1000 ^® Growth Index (as of December 31, 2011, this range was between approximately $117 million and $401.25 billion)) at the time of purchase. The Fund invests in growth equity securities; growth orientation emphasizes buying equity securities of companies whose potential for growth of capital and earnings is expected to be above average.

XML

MidCap Blend Fund (Prospectus Summary): | MidCap Blend Fund

MidCap Blend Fund  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with medium market capitalizations (those with market capitalizations similar to companies in the Russell Midcap ^® Index (as of December 31, 2011, this range was between approximately $117 million and $20.51 billion) at the time of purchase. The Fund may invest in foreign securities.

XML

SmallCap Value Fund II (Prospectus Summary): | SmallCap Value Fund II

SmallCap Value Fund II  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of U.S. companies with small market capitalizations (those with market capitalizations similar to companies in the Russell 2000 ^® Value Index (as of December 31, 2011, this range was between approximately $20 million and $3.7 billion)) or in securities with market capitalizations of $3.5 billion or less at the time of purchase. The Fund invests in value equity securities, an investment strategy that emphasizes buying equity securities that appear to be undervalued. The Fund will also invest in real estate investment trusts.

XML

MidCap Value Fund I (Prospectus Summary): | MidCap Value Fund I

MidCap Value Fund I  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in a diversified portfolio of equity securities of companies with a medium market capitalization (those with market capitalizations similar to companies in the Russell Midcap ^® Value Index (as of December 31, 2011, the range was between approximately $117 million and $20.51 billion)) at the time of purchase. The Fund invests in value equity securities, an investment strategy that emphasizes buying equity securities that appear to be undervalued. The Fund will also invest in real estate investment trusts.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

MidCap Blend Fund (Prospectus Summary): | MidCap Blend Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

MidCap Blend Fund  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with medium market capitalizations (those with market capitalizations similar to companies in the Russell Midcap ^® Index (as of December 31, 2011, this range was between approximately $117 million and $20.51 billion) at the time of purchase. The Fund may invest in foreign securities.

MidCap Blend Fund | R-1

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PMSBX

MidCap Blend Fund | R-2

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PMBNX

MidCap Blend Fund | R-3

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PMBMX

MidCap Blend Fund | R-5

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PMBPX

MidCap Blend Fund | R-4

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PMBSX

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

LargeCap Growth Fund (Prospectus Summary): | LargeCap Growth Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

LargeCap Growth Fund  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with large market capitalizations (those with market capitalizations similar to companies in the Russell 1000 ^® Growth Index (as of December 31, 2011, this range was between approximately $117 million and $401.25 billion)) at the time of purchase. The Fund invests in growth equity securities; growth orientation emphasizes buying equity securities of companies whose potential for growth of capital and earnings is expected to be above average.

LargeCap Growth Fund | R-2

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PCPPX

LargeCap Growth Fund | R-3

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PLGPX

LargeCap Growth Fund | R-5

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PDPPX

LargeCap Growth Fund | R-4

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PEPPX

LargeCap Growth Fund | R-1

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PLSGX

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

LargeCap Value Fund III (Prospectus Summary): | LargeCap Value Fund III

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

LargeCap Value Fund III  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in companies with large market capitalizations similar to companies in the Russell 1000 ^® Value Index (approximately $117 million to $401.25 billion as of December 31, 2011) at the time of purchase. The Fund invests in value equity securities, an investment strategy that emphasizes buying equity securities that appear to be undervalued.

LargeCap Value Fund III | R-1

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PESAX

LargeCap Value Fund III | R-2

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPSNX

LargeCap Value Fund III | R-3

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPSFX

LargeCap Value Fund III | R-5

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPSRX

LargeCap Value Fund III | R-4

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPSSX

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	Other
Document Period End Date	dei_DocumentPeriodEndDate	Sep. 14, 2012
Registrant Name	dei_EntityRegistrantName	PRINCIPAL FUNDS INC
Central Index Key	dei_EntityCentralIndexKey	0000898745
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Sep. 14, 2012
Document Effective Date	dei_DocumentEffectiveDate	Sep. 14, 2012
Prospectus Date	rr_ProspectusDate	Feb. 29, 2012

XML

LargeCap Value Fund I (Prospectus Summary): | LargeCap Value Fund I

LargeCap Value Fund I  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in securities of companies with large market capitalizations (those with market capitalizations similar to companies in the Russell 1000 ^® Value Index (as of December 31, 2011, this range was between approximately $117 million and $401.25 billion)) at the time of purchase. The Fund invests in value equity securities, an investment strategy that emphasizes buying equity securities that appear to be undervalued.

XML

LargeCap Value Fund (Prospectus Summary): | LargeCap Value Fund

LargeCap Value Fund  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with large market capitalizations (those with market capitalizations similar to companies in the Russell 1000 ^® Value Index, which as of December 31, 2011 ranged between approximately $117 million and $401.25 billion) at the time of purchase. The Fund invests in value equity securities, an investment strategy that emphasizes buying equity securities that appear to be undervalued. The Fund may actively trade portfolio securities.

XML

MidCap Value Fund III (Prospectus Summary): | MidCap Value Fund III

MidCap Value Fund III  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with medium market capitalizations (those with market capitalizations similar to companies in the Russell Midcap ^® Value Index (as of December 31, 2011, this range was between approximately $117 million and $20.51 billion)) at the time of purchase. The Fund invests in value equity securities, an investment strategy that emphasizes buying equity securities that appear to be undervalued. The Fund may invest in real estate investment trusts.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

MidCap Growth Fund (Prospectus Summary): | MidCap Growth Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

MidCap Growth Fund  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with medium market capitalizations (those with market capitalizations similar to companies in the Russell Midcap ^® Growth Index (as of December 31, 2011, this range was between approximately $117 million and $20.51 billion)) at the time of purchase. The Fund invests in growth equity securities; growth orientation emphasizes buying equity securities of companies whose potential for growth of capital and earnings is expected to be above average. The Fund may actively trade portfolio securities and invest its assets in the securities of foreign issuers.

MidCap Growth Fund | R-2

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PGPPX

MidCap Growth Fund | R-3

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PFPPX

MidCap Growth Fund | R-5

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PHPPX

MidCap Growth Fund | R-4

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PIPPX

MidCap Growth Fund | R-1

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PMSGX

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

SmallCap Value Fund II (Prospectus Summary): | SmallCap Value Fund II

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

SmallCap Value Fund II  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of U.S. companies with small market capitalizations (those with market capitalizations similar to companies in the Russell 2000 ^® Value Index (as of December 31, 2011, this range was between approximately $20 million and $3.7 billion)) or in securities with market capitalizations of $3.5 billion or less at the time of purchase. The Fund invests in value equity securities, an investment strategy that emphasizes buying equity securities that appear to be undervalued. The Fund will also invest in real estate investment trusts.

SmallCap Value Fund II | R-2

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PKARX

SmallCap Value Fund II | R-3

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PJARX

SmallCap Value Fund II | R-5

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PLARX

SmallCap Value Fund II | R-4

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PSTWX

SmallCap Value Fund II | R-1

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PCPTX

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

LargeCap Value Fund I (Prospectus Summary): | LargeCap Value Fund I

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

LargeCap Value Fund I  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in securities of companies with large market capitalizations (those with market capitalizations similar to companies in the Russell 1000 ^® Value Index (as of December 31, 2011, this range was between approximately $117 million and $401.25 billion)) at the time of purchase. The Fund invests in value equity securities, an investment strategy that emphasizes buying equity securities that appear to be undervalued.

LargeCap Value Fund I | R-2

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PABEX

LargeCap Value Fund I | R-3

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PABDX

LargeCap Value Fund I | R-5

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PAFBX

LargeCap Value Fund I | R-4

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PAGBX

LargeCap Value Fund I | R-1

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PVUAX

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

LargeCap Growth Fund II (Prospectus Summary): | LargeCap Growth Fund II

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

LargeCap Growth Fund II  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with large market capitalizations (those with market capitalizations similar to companies in the Russell 1000 ^® Growth Index (as of December 31, 2011, the range was between approximately $117 million and $401.25 billion)) at the time of purchase. The Fund invests in growth equity securities; growth orientation emphasizes buying equity securities of companies whose potential for growth of capital and earnings is expected to be above average.

LargeCap Growth Fund II | R-1

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PDASX

LargeCap Growth Fund II | R-2

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPTNX

LargeCap Growth Fund II | R-3

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPTMX

LargeCap Growth Fund II | R-5

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPTPX

LargeCap Growth Fund II | R-4

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPTSX

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

MidCap Value Fund III (Prospectus Summary): | MidCap Value Fund III

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

MidCap Value Fund III  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with medium market capitalizations (those with market capitalizations similar to companies in the Russell Midcap ^® Value Index (as of December 31, 2011, this range was between approximately $117 million and $20.51 billion)) at the time of purchase. The Fund invests in value equity securities, an investment strategy that emphasizes buying equity securities that appear to be undervalued. The Fund may invest in real estate investment trusts.

MidCap Value Fund III | R-2

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PKPPX

MidCap Value Fund III | R-3

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PJPPX

MidCap Value Fund III | R-5

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PLPPX

MidCap Value Fund III | R-4

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PMPPX

MidCap Value Fund III | R-1

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PMSVX

XML

LargeCap Growth Fund II (Prospectus Summary): | LargeCap Growth Fund II

LargeCap Growth Fund II  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with large market capitalizations (those with market capitalizations similar to companies in the Russell 1000 ^® Growth Index (as of December 31, 2011, the range was between approximately $117 million and $401.25 billion)) at the time of purchase. The Fund invests in growth equity securities; growth orientation emphasizes buying equity securities of companies whose potential for growth of capital and earnings is expected to be above average.

XML

LargeCap Value Fund III (Prospectus Summary): | LargeCap Value Fund III

LargeCap Value Fund III  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in companies with large market capitalizations similar to companies in the Russell 1000 ^® Value Index (approximately $117 million to $401.25 billion as of December 31, 2011) at the time of purchase. The Fund invests in value equity securities, an investment strategy that emphasizes buying equity securities that appear to be undervalued.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

MidCap Growth Fund III (Prospectus Summary): | MidCap Growth Fund III

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

MidCap Growth Fund III  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with medium market capitalizations (those with market capitalizations similar to companies in the Russell Midcap ^® Growth Index (as of December 31, 2011, this range was between approximately $117 million and $20.51 billion)) at the time of purchase. The Fund invests in growth equity securities; growth orientation emphasizes buying equity securities of companies whose potential for growth of capital and earnings is expected to be above average. The Fund may actively trade portfolio securities.

MidCap Growth Fund III | R-1

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PHASX

MidCap Growth Fund III | R-2

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPQNX

MidCap Growth Fund III | R-3

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPQMX

MidCap Growth Fund III | R-5

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPQPX

MidCap Growth Fund III | R-4

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPQSX

XML

SmallCap Growth Fund I (Prospectus Summary): | SmallCap Growth Fund I

SmallCap Growth Fund I  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with small market capitalizations (those with market capitalizations equal to or smaller than the greater of: 1) $4.0 billion or 2) the highest market capitalization of the companies in the Russell 2000 ^® Growth Index (as of December 31, 2011, the range was between approximately $23 million and $3.7 billion)) at the time of purchase. The Fund invests in growth equity securities; growth orientation emphasizes buying equity securities of companies whose potential for growth of capital and earnings is expected to be above average.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

LargeCap Value Fund (Prospectus Summary): | LargeCap Value Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

LargeCap Value Fund  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with large market capitalizations (those with market capitalizations similar to companies in the Russell 1000 ^® Value Index, which as of December 31, 2011 ranged between approximately $117 million and $401.25 billion) at the time of purchase. The Fund invests in value equity securities, an investment strategy that emphasizes buying equity securities that appear to be undervalued. The Fund may actively trade portfolio securities.

LargeCap Value Fund | R-1

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PLSVX

LargeCap Value Fund | R-2

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PLVNX

LargeCap Value Fund | R-3

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PLVMX

LargeCap Value Fund | R-5

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PLVPX

LargeCap Value Fund | R-4

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PLVSX

XML

MidCap Growth Fund (Prospectus Summary): | MidCap Growth Fund

MidCap Growth Fund  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with medium market capitalizations (those with market capitalizations similar to companies in the Russell Midcap ^® Growth Index (as of December 31, 2011, this range was between approximately $117 million and $20.51 billion)) at the time of purchase. The Fund invests in growth equity securities; growth orientation emphasizes buying equity securities of companies whose potential for growth of capital and earnings is expected to be above average. The Fund may actively trade portfolio securities and invest its assets in the securities of foreign issuers.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Feb. 29, 2012

SmallCap Growth Fund I (Prospectus Summary): | SmallCap Growth Fund I

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

SmallCap Growth Fund I  

Supplement Text

ck0000898745_SupplementTextBlock

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Investment Strategy, Heading

rr_StrategyHeading

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with small market capitalizations (those with market capitalizations equal to or smaller than the greater of: 1) $4.0 billion or 2) the highest market capitalization of the companies in the Russell 2000 ^® Growth Index (as of December 31, 2011, the range was between approximately $23 million and $3.7 billion)) at the time of purchase. The Fund invests in growth equity securities; growth orientation emphasizes buying equity securities of companies whose potential for growth of capital and earnings is expected to be above average.

SmallCap Growth Fund I | R-1

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PNASX

SmallCap Growth Fund I | R-2

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPNNX

SmallCap Growth Fund I | R-3

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPNMX

SmallCap Growth Fund I | R-5

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPNPX

SmallCap Growth Fund I | R-4

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

PPNSX

XML

MidCap Growth Fund III (Prospectus Summary): | MidCap Growth Fund III

MidCap Growth Fund III  

Supplement dated September 14, 2012

to the Class R-1, Class R-2, Class R-3, Class R-4 and Class R-5 Shares Prospectus

for Principal Funds, Inc.

dated February 29, 2012

(as supplemented on March 16, 2012, April 23, 2012, June 15, 2012, and July 17, 2012)

This supplement updates information currently in the Prospectus. Retain this supplement with the Prospectus.

FUND SUMMARIES

Under the Principal Investment Strategies heading, delete the first paragraph and substitute:  

Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in equity securities of companies with medium market capitalizations (those with market capitalizations similar to companies in the Russell Midcap ^® Growth Index (as of December 31, 2011, this range was between approximately $117 million and $20.51 billion)) at the time of purchase. The Fund invests in growth equity securities; growth orientation emphasizes buying equity securities of companies whose potential for growth of capital and earnings is expected to be above average. The Fund may actively trade portfolio securities.