485BPOS

As filed electronically with the Securities and Exchange Commission on October 4, 2012.

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

Registration No. 033-00507

Pre-Effective Amendment No.

Post-Effective Amendment No.  115

and/or

REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940

1940 Act File No. 811-04419

Amendment No.            116

(Check appropriate box or boxes.)

Transamerica Series Trust

(Exact Name of Registrant as Specified in Charter)

570 Carillon Parkway, St. Petersburg, Florida 33716

(Address of Principal Executive Offices) (Zip Code)

Registrant’s Telephone Number, including Area Code:    (727) 299-1800

Dennis P. Gallagher, Esq. 570 Carillon Parkway St. Petersburg, Florida 33716

(Name and Address of Agent for Service)

Approximate date of proposed public offering:

It is proposed that this filing will become effective:

¨ 60 days after filing pursuant to paragraph (a) (1) of Rule 485.

¨ 75 days after filing pursuant to paragraph (a) (2) of Rule 485.

¨ On (Date) pursuant to paragraph (a) (1) of Rule 485.

¨ On (Date) pursuant to paragraph (a) (2) of Rule 485.

x Immediately upon filing pursuant to paragraph (b) of Rule 485.

¨ On (Date) pursuant to paragraph (b) of Rule 485.

If appropriate, check the following box:

¨ This post-effective amendment designates a new effective date for a previously filed post-effective amendment.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all of the requirements for effectiveness of this Registration Statement pursuant to Rule 485(b) under the Securities Act of 1933; and Transamerica Series Trust has duly caused this Post-Effective Amendment No. 115 to its Registration Statement to be signed on its behalf by the undersigned, thereunder duly authorized, in the City of St. Petersburg, State of Florida, on the 4^th day of October, 2012.

TRANSAMERICA SERIES TRUST
By:	/s/ Thomas A. Swank
	Thomas A. Swank
	President and Chief Executive Officer

Pursuant to the requirements of the Securities Act of 1933, this Post-Effective Amendment No.  115 to its Registration Statement has been signed below by the following persons in the capacities and on the dates indicated:

/s/ Thomas A. Swank Thomas A. Swank	President and Chief Executive Officer	October 4, 2012
/s/ Sandra N. Bane Sandra N. Bane*	Trustee	October 4, 2012
/s/ Leo J. Hill Leo J. Hill*	Trustee	October 4, 2012
/s/ David W. Jennings David W. Jennings*	Trustee	October 4, 2012
/s/ Russell A. Kimball, Jr. Russell A. Kimball, Jr.*	Trustee	October 4, 2012
/s/ Eugene M. Mannella Eugene M. Mannella*	Trustee	October 4, 2012
/s/ Norman R. Nielsen Norman R. Nielsen*	Trustee	October 4, 2012
/s/ Joyce G. Norden Joyce G. Norden*	Trustee	October 4, 2012
/s/ Patricia L. Sawyer Patricia L. Sawyer*	Trustee	October 4, 2012
/s/ John W. Waechter John W. Waechter*	Trustee	October 4, 2012
/s/ Alan F. Warrick Alan F. Warrick*	Trustee	October 4, 2012
/s/ Elizabeth Strouse Elizabeth Strouse	Vice President, Treasurer and Principal Financial Officer	October 4, 2012
/s/ Dennis P. Gallagher		October 4, 2012
* By: Dennis P. Gallagher
Dennis P. Gallagher**

** Attorney-in-fact pursuant to powers of attorney previously filed.

WASHINGTON, D.C. 20549

SECURITIES AND EXCHANGE COMMISSION

Exhibits Filed With

Post-Effective Amendment No. 115 to

Registration Statement on

Form N-1A

Transamerica Series Trust

Registration No. 033-00507

EXHIBIT INDEX

Exhibits	Description of Exhibits
EX-101.INS	XBRL Instance Document
EX-101.CAL	XBRL Taxonomy Calculation Linkbase Document
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase Document
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.PRE	XBRL Taxonomy Presentation Linkbase Document

XML

Transamerica Market Participation Strategy VP

TRANSAMERICA MARKET PARTICIPATION STRATEGY VP

Investment Objective:

Seeks capital appreciation.

Fees and Expenses:

This table describes the fees and expenses that you may pay if you buy and hold portfolio shares, but it does not reflect any charges that are, or may be, imposed under your variable life insurance policy or variable annuity contract. If such charges were reflected, fees would be higher.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Transamerica Market Participation Strategy VP	Initial Class	Service Class
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	none	none
Maximum deferred sales charge (load) (as a percentage of purchase price or redemption proceeds, whichever is lower)	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your
investment)

Annual Fund Operating Expenses Transamerica Market Participation Strategy VP		Initial Class	Service Class
Management fees		0.65%	0.65%
Distribution and service (12b-1) fees		none	0.25%
Other expenses	[1]	0.07%	0.07%
Total annual fund operating expenses		0.72%	0.97%

Example:

This Example is intended to help you compare the cost of investing in the portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the portfolio for the time periods indicated and then redeem all shares at the end of those periods (unless otherwise indicated). The Example also assumes that your investment has a 5% return each year and that the portfolio's operating expenses remain the same. The Example does not reflect charges that are, or may be, imposed under your variable life insurance policy or variable annuity contract. If such charges were reflected, costs would be higher. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Transamerica Market Participation Strategy VP (USD $)	1 year	3 years
Initial Class	74	263
Service Class	99	309

Portfolio Turnover:

The portfolio pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the portfolio's performance.

Principal Investment Strategies:

The portfolio attempts to provide upside participation in the stock market when the stock market advances and to reduce declines in the portfolio's value when the stock market declines.

The strategy is designed to provide upside equity participation similar to 42% equity exposure while seeking to reduce downside risk over the course of a full market cycle. The portfolio will not invest directly in equity securities. The portfolio will gain equity exposure through investments in S&P 500 Index options and futures. The portfolio will also invest in U.S. Treasuries and U.S. agency bonds.

The portfolio's sub-adviser, Quantitative Management Associates LLC (the "sub-adviser") will periodically rebalance the asset mix of U.S. Treasuries, U.S. agency bonds, and equity index options and futures to respond to changing market conditions and to achieve what it believes to be the optimal balance between risk and reward. When determining the allocation and when to rebalance, the sub-adviser will take into account, among other factors: interest rates, the portfolio's equity exposure, the percentage of the portfolio invested in options, the current level of the S&P 500 Index, the volatility of S&P 500 Index options, bond and dividend yields, the delta of the portfolio's options positions (which is a measure of the sensitivity of the portfolio's option prices to changes in price of the S&P 500 Index), and time to maturity of the options. The sub-adviser will also consider internal research generated by its asset allocation team when evaluating the relative attractiveness of stocks versus bonds.

There are no limitations on the amounts of the portfolio's assets that may be invested in fixed income or equity investments.

The portfolio is non-diversified.

Under adverse or unstable market, economic or political conditions, the portfolio may take temporary defensive positions in cash and short-term debt securities without limit. During periods of defensive investing, it will be more difficult for the portfolio to achieve its objective.

Principal Risks:

Risk is inherent in all investing. Many factors affect the portfolio's performance. There is no assurance the portfolio will meet its investment objective. The value of your investment in the portfolio, as well as the amount of return you receive on your investment, may fluctuate significantly. You may lose part or all of your investment in the portfolio or your investment may not perform as well as other similar investments. The following is a summary description of principal risks (in alphabetical order) of investing in the portfolio. You may lose money if you invest in this portfolio.

• Cash Management and Defensive Investing – Money market instruments or short-term debt securities held by the portfolio for cash management or defensive investing purposes can fluctuate in value. Like other fixed income securities, they are subject to risk, including market, interest rate and credit risk. If the portfolio holds cash uninvested, the portfolio will be subject to the credit risk of the depository institution holding the cash, it will not earn income on the cash and the portfolio's yield will go down. To the extent that the portfolio's assets are used for cash management or defensive investing purposes, it will be more difficult for the portfolio to achieve its objective.

• Credit – If an issuer or guarantor of a security held by the portfolio or a counterparty to a financial contract with the portfolio defaults or is downgraded, or is perceived to be less creditworthy, or if the credit quality or value of any underlying assets declines, the value of your investment will decline.

• Derivatives – Using derivatives exposes the portfolio to additional risks and can increase portfolio losses and reduce opportunities for gains when market prices, interest rates or the derivative instruments themselves behave in a way not anticipated by the portfolio. Using derivatives also can have a leveraging effect and increase portfolio volatility. The portfolio may also have to sell assets at inopportune times to satisfy its obligations. Derivatives may be difficult to sell, unwind or value, and the counterparty may default on its obligations to the portfolio. The portfolio's investments in derivative instruments may involve a small investment relative to the amount of investment exposure assumed and may result in losses exceeding the amounts invested in those instruments. Recent legislation calls for new regulation of the derivatives markets. The extent and impact of the regulation are not yet fully known and may not be for some time. New regulation of derivatives may make them more costly, may limit their availability, or may otherwise adversely affect their value or performance.

• Equity Securities – Equity securities represent an ownership interest in an issuer, rank junior in a company's capital structure and consequently may entail greater risk of loss than debt securities. Equity securities include common and preferred stocks. Stock markets are volatile. The price of equity securities fluctuates based on changes in a company's financial condition and overall market and economic conditions. If the market prices of the equity securities owned by the portfolio fall, the value of your investment in the portfolio will decline.

• Expenses – Your actual costs of investing in the portfolio may be higher than the expenses shown in this prospectus for a variety of reasons. For example, expense ratios may be higher than those shown if overall net assets decrease. Net assets are more likely to decrease and portfolio expense ratios are more likely to increase when markets are volatile.

• Extension – If interest rates rise, repayments of fixed income securities may occur more slowly than anticipated by the market. This may drive the prices of these securities down because their interest rates are lower than the current interest rate and they remain outstanding longer.

• Interest Rate – Interest rates may go up, causing the value of the portfolio's investments to decline. Debt securities have varying levels of sensitivity to changes in interest rates. A rise in rates tends to have a greater impact on the prices of longer term or duration securities.

• Manager – The sub-adviser to the portfolio actively manages the portfolio's investments. Consequently, the portfolio is subject to the risk that the methods and analyses employed by the sub-adviser in this process may not produce the desired results. This could cause the portfolio to lose value or its results to lag relevant benchmarks or other funds with similar objectives.

• Market – The market prices of the portfolio's securities may go down, sometimes rapidly or unpredictably, due to general market conditions, such as real or perceived adverse economic or political conditions, inflation, changes in interest rates or currency rates, lack of liquidity in the markets or adverse investor sentiment. Adverse market conditions may be prolonged and may not have the same impact on all types of securities. Market prices of securities also may go down due to events or conditions that affect particular sectors, industries or issuers. When market prices fall, the value of your investment will go down. The portfolio may experience a substantial or complete loss on any individual security. The financial crisis that began in 2008 has caused a significant decline in the value and liquidity of many securities. In response to the financial crisis, the U.S. and other governments and the Federal Reserve and certain foreign central banks have taken steps to support financial markets. The withdrawal of this support could negatively affect the value and liquidity of certain securities. In addition, legislation recently enacted in the U.S. is changing many aspects of financial regulation. The impact of the legislation on the markets, and the practical implications for market participants, may not be fully known for some time.

• Non-Diversification – The portfolio is classified as "non-diversified," which means it may invest a larger percentage of its assets in a smaller number of issuers than a diversified fund. To the extent the portfolio invests its assets in fewer issuers, the portfolio will be more susceptible to negative events affecting those issuers.

• Prepayment or Call – Many issuers have a right to prepay their securities. If interest rates fall, an issuer may exercise this right. If this happens, the portfolio will be forced to reinvest prepayment proceeds at a time when yields on securities available in the market are lower than the yield on the prepaid security. The portfolio also may lose any premium it paid on the security.

• Tactical Asset Allocation – Tactical asset allocation is an investment strategy that actively adjusts a portfolio's asset allocation. The portfolio's tactical asset management discipline may not work as intended. The portfolio may not achieve its objective and may not perform as well as other funds using other asset management styles, including those based on fundamental analysis (a method of evaluating a security that entails attempting to measure its intrinsic value by examining related economic, financial and other factors) or strategic asset allocation (a strategy that involves periodically rebalancing the portfolio in order to maintain a long-term goal for asset allocation). The sub-adviser's evaluations and assumptions in selecting underlying funds or individual securities may be incorrect in view of actual market conditions, and may result in owning securities that underperform other securities.

• U.S. Government Agency Obligations – Government agency obligations have different levels of credit support and, therefore, different degrees of credit risk. Securities issued by agencies and instrumentalities of the U.S. government that are supported by the full faith and credit of the United States generally present a lesser degree of credit risk than securities issued by agencies and instrumentalities sponsored by the U.S. government that are supported only by the issuer's right to borrow from the U.S. Treasury and securities issued by agencies and instrumentalities sponsored by the U.S. government that are supported only by the credit of the issuing agencies. Although the U.S. government has provided financial support to the Federal National Mortgage Association (Fannie Mae) and the Federal Home Loan Mortgage Corporation (Freddie Mac) in the past, there can be no assurance that it will support these or other government sponsored entities in the future.

• Zero Coupon Bonds – Zero coupon bonds pay no interest during the life of the obligation but trade at prices below their stated maturity value. Although these securities lock in a rate of return to maturity, they may be subject to greater fluctuations in market value than securities that pay interest periodically.

Performance:

No performance is shown for the portfolio. Performance information will appear in a future version of this prospectus once the portfolio has a full calendar year of performance information to report to investors.

[1] Other expenses are based on estimates for the current fiscal year.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

TRANSAMERICA SERIES TRUST

Prospectus Date

rr_ProspectusDate

Sep. 17, 2012

Transamerica Market Participation Strategy VP

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

TRANSAMERICA MARKET PARTICIPATION STRATEGY VP

Objective [Heading]

rr_ObjectiveHeading

Investment Objective:

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Seeks capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses:

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold portfolio shares, but it does not reflect any charges that are, or may be, imposed under your variable life insurance policy or variable annuity contract. If such charges were reflected, fees would be higher.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your
investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The portfolio pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the portfolio's performance.

Other Expenses, New Fund, Based on Estimates [Text]

rr_OtherExpensesNewFundBasedOnEstimates

Other expenses are based on estimates for the current fiscal year.

Expense Example [Heading]

rr_ExpenseExampleHeading

Example:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the portfolio for the time periods indicated and then redeem all shares at the end of those periods (unless otherwise indicated). The Example also assumes that your investment has a 5% return each year and that the portfolio's operating expenses remain the same. The Example does not reflect charges that are, or may be, imposed under your variable life insurance policy or variable annuity contract. If such charges were reflected, costs would be higher. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies:

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The portfolio attempts to provide upside participation in the stock market when the stock market advances and to reduce declines in the portfolio's value when the stock market declines.

The strategy is designed to provide upside equity participation similar to 42% equity exposure while seeking to reduce downside risk over the course of a full market cycle. The portfolio will not invest directly in equity securities. The portfolio will gain equity exposure through investments in S&P 500 Index options and futures. The portfolio will also invest in U.S. Treasuries and U.S. agency bonds.

The portfolio's sub-adviser, Quantitative Management Associates LLC (the "sub-adviser") will periodically rebalance the asset mix of U.S. Treasuries, U.S. agency bonds, and equity index options and futures to respond to changing market conditions and to achieve what it believes to be the optimal balance between risk and reward. When determining the allocation and when to rebalance, the sub-adviser will take into account, among other factors: interest rates, the portfolio's equity exposure, the percentage of the portfolio invested in options, the current level of the S&P 500 Index, the volatility of S&P 500 Index options, bond and dividend yields, the delta of the portfolio's options positions (which is a measure of the sensitivity of the portfolio's option prices to changes in price of the S&P 500 Index), and time to maturity of the options. The sub-adviser will also consider internal research generated by its asset allocation team when evaluating the relative attractiveness of stocks versus bonds.

There are no limitations on the amounts of the portfolio's assets that may be invested in fixed income or equity investments.

The portfolio is non-diversified.

Under adverse or unstable market, economic or political conditions, the portfolio may take temporary defensive positions in cash and short-term debt securities without limit. During periods of defensive investing, it will be more difficult for the portfolio to achieve its objective.

Risk [Heading]

rr_RiskHeading

Principal Risks:

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

Risk is inherent in all investing. Many factors affect the portfolio's performance. There is no assurance the portfolio will meet its investment objective. The value of your investment in the portfolio, as well as the amount of return you receive on your investment, may fluctuate significantly. You may lose part or all of your investment in the portfolio or your investment may not perform as well as other similar investments. The following is a summary description of principal risks (in alphabetical order) of investing in the portfolio. You may lose money if you invest in this portfolio.

• Cash Management and Defensive Investing – Money market instruments or short-term debt securities held by the portfolio for cash management or defensive investing purposes can fluctuate in value. Like other fixed income securities, they are subject to risk, including market, interest rate and credit risk. If the portfolio holds cash uninvested, the portfolio will be subject to the credit risk of the depository institution holding the cash, it will not earn income on the cash and the portfolio's yield will go down. To the extent that the portfolio's assets are used for cash management or defensive investing purposes, it will be more difficult for the portfolio to achieve its objective.

• Credit – If an issuer or guarantor of a security held by the portfolio or a counterparty to a financial contract with the portfolio defaults or is downgraded, or is perceived to be less creditworthy, or if the credit quality or value of any underlying assets declines, the value of your investment will decline.

• Derivatives – Using derivatives exposes the portfolio to additional risks and can increase portfolio losses and reduce opportunities for gains when market prices, interest rates or the derivative instruments themselves behave in a way not anticipated by the portfolio. Using derivatives also can have a leveraging effect and increase portfolio volatility. The portfolio may also have to sell assets at inopportune times to satisfy its obligations. Derivatives may be difficult to sell, unwind or value, and the counterparty may default on its obligations to the portfolio. The portfolio's investments in derivative instruments may involve a small investment relative to the amount of investment exposure assumed and may result in losses exceeding the amounts invested in those instruments. Recent legislation calls for new regulation of the derivatives markets. The extent and impact of the regulation are not yet fully known and may not be for some time. New regulation of derivatives may make them more costly, may limit their availability, or may otherwise adversely affect their value or performance.

• Equity Securities – Equity securities represent an ownership interest in an issuer, rank junior in a company's capital structure and consequently may entail greater risk of loss than debt securities. Equity securities include common and preferred stocks. Stock markets are volatile. The price of equity securities fluctuates based on changes in a company's financial condition and overall market and economic conditions. If the market prices of the equity securities owned by the portfolio fall, the value of your investment in the portfolio will decline.

• Expenses – Your actual costs of investing in the portfolio may be higher than the expenses shown in this prospectus for a variety of reasons. For example, expense ratios may be higher than those shown if overall net assets decrease. Net assets are more likely to decrease and portfolio expense ratios are more likely to increase when markets are volatile.

• Extension – If interest rates rise, repayments of fixed income securities may occur more slowly than anticipated by the market. This may drive the prices of these securities down because their interest rates are lower than the current interest rate and they remain outstanding longer.

• Interest Rate – Interest rates may go up, causing the value of the portfolio's investments to decline. Debt securities have varying levels of sensitivity to changes in interest rates. A rise in rates tends to have a greater impact on the prices of longer term or duration securities.

• Manager – The sub-adviser to the portfolio actively manages the portfolio's investments. Consequently, the portfolio is subject to the risk that the methods and analyses employed by the sub-adviser in this process may not produce the desired results. This could cause the portfolio to lose value or its results to lag relevant benchmarks or other funds with similar objectives.

• Market – The market prices of the portfolio's securities may go down, sometimes rapidly or unpredictably, due to general market conditions, such as real or perceived adverse economic or political conditions, inflation, changes in interest rates or currency rates, lack of liquidity in the markets or adverse investor sentiment. Adverse market conditions may be prolonged and may not have the same impact on all types of securities. Market prices of securities also may go down due to events or conditions that affect particular sectors, industries or issuers. When market prices fall, the value of your investment will go down. The portfolio may experience a substantial or complete loss on any individual security. The financial crisis that began in 2008 has caused a significant decline in the value and liquidity of many securities. In response to the financial crisis, the U.S. and other governments and the Federal Reserve and certain foreign central banks have taken steps to support financial markets. The withdrawal of this support could negatively affect the value and liquidity of certain securities. In addition, legislation recently enacted in the U.S. is changing many aspects of financial regulation. The impact of the legislation on the markets, and the practical implications for market participants, may not be fully known for some time.

• Non-Diversification – The portfolio is classified as "non-diversified," which means it may invest a larger percentage of its assets in a smaller number of issuers than a diversified fund. To the extent the portfolio invests its assets in fewer issuers, the portfolio will be more susceptible to negative events affecting those issuers.

• Prepayment or Call – Many issuers have a right to prepay their securities. If interest rates fall, an issuer may exercise this right. If this happens, the portfolio will be forced to reinvest prepayment proceeds at a time when yields on securities available in the market are lower than the yield on the prepaid security. The portfolio also may lose any premium it paid on the security.

• Tactical Asset Allocation – Tactical asset allocation is an investment strategy that actively adjusts a portfolio's asset allocation. The portfolio's tactical asset management discipline may not work as intended. The portfolio may not achieve its objective and may not perform as well as other funds using other asset management styles, including those based on fundamental analysis (a method of evaluating a security that entails attempting to measure its intrinsic value by examining related economic, financial and other factors) or strategic asset allocation (a strategy that involves periodically rebalancing the portfolio in order to maintain a long-term goal for asset allocation). The sub-adviser's evaluations and assumptions in selecting underlying funds or individual securities may be incorrect in view of actual market conditions, and may result in owning securities that underperform other securities.

• U.S. Government Agency Obligations – Government agency obligations have different levels of credit support and, therefore, different degrees of credit risk. Securities issued by agencies and instrumentalities of the U.S. government that are supported by the full faith and credit of the United States generally present a lesser degree of credit risk than securities issued by agencies and instrumentalities sponsored by the U.S. government that are supported only by the issuer's right to borrow from the U.S. Treasury and securities issued by agencies and instrumentalities sponsored by the U.S. government that are supported only by the credit of the issuing agencies. Although the U.S. government has provided financial support to the Federal National Mortgage Association (Fannie Mae) and the Federal Home Loan Mortgage Corporation (Freddie Mac) in the past, there can be no assurance that it will support these or other government sponsored entities in the future.

• Zero Coupon Bonds – Zero coupon bonds pay no interest during the life of the obligation but trade at prices below their stated maturity value. Although these securities lock in a rate of return to maturity, they may be subject to greater fluctuations in market value than securities that pay interest periodically.

Risk Lose Money [Text]

rr_RiskLoseMoney

You may lose money if you invest in this portfolio.

Risk Nondiversified Status [Text]

rr_RiskNondiversifiedStatus

Non-Diversification – The portfolio is classified as "non-diversified," which means it may invest a larger percentage of its assets in a smaller number of issuers than a diversified fund. To the extent the portfolio invests its assets in fewer issuers, the portfolio will be more susceptible to negative events affecting those issuers.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance:

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

No performance is shown for the portfolio. Performance information will appear in a future version of this prospectus once the portfolio has a full calendar year of performance information to report to investors.

Performance One Year or Less [Text]

rr_PerformanceOneYearOrLess

Performance information will appear in a future version of this prospectus once the portfolio has a full calendar year of performance information to report to investors.

Transamerica Market Participation Strategy VP | Initial Class

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) (as a percentage of purchase price or redemption proceeds, whichever is lower)

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.65%

Distribution and service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.07%

^[1]

Total annual fund operating expenses

rr_ExpensesOverAssets

0.72%

1 year

rr_ExpenseExampleYear01

74

3 years

rr_ExpenseExampleYear03

263

Transamerica Market Participation Strategy VP | Service Class

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) (as a percentage of purchase price or redemption proceeds, whichever is lower)

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.65%

Distribution and service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.07%

^[1]

Total annual fund operating expenses

rr_ExpensesOverAssets

0.97%

1 year

rr_ExpenseExampleYear01

99

3 years

rr_ExpenseExampleYear03

309

[1] Other expenses are based on estimates for the current fiscal year.

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Registrant Name	dei_EntityRegistrantName	TRANSAMERICA SERIES TRUST
Prospectus Date	rr_ProspectusDate	Sep. 17, 2012
Document Creation Date	dei_DocumentCreationDate	Sep. 07, 2012

XML

Document and Entity Information	12 Months Ended
	Sep. 17, 2012
Risk/Return:
Document Type	485BPOS
Document Period End Date	Sep. 07, 2012
Registrant Name	TRANSAMERICA SERIES TRUST
Central Index Key	0000778207
Amendment Flag	false
Document Creation Date	Sep. 07, 2012
Document Effective Date	Sep. 17, 2012
Prospectus Date	Sep. 17, 2012