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.