0001521894 2011-09-01 2012-08-31 0001521894 gmost1:S000035217Member 2011-09-01 2012-08-31 GMO Series Trust Other 2012-04-30 false 2012-09-11 0001521894 2012-09-11 2012-08-31 GMO SERIES TRUST Supplement dated September 11, 2012 to GMO Series Trust Prospectus and Statement of Additional Information, each dated August 31, 2012 GMO Global Asset Allocation Series Fund The reference to the benchmark of GMO Global Asset Allocation Series Fund that appears in the Average Annual Total Returns table on page 69 of the Prospectus is amended to "GMO Global Asset Allocation Index." GMO SERIES TRUST Supplement dated September 11, 2012 to GMO Series Trust Prospectus and Statement of Additional Information, each dated August 31, 2012 GMO Global Asset Allocation Series Fund The reference to the benchmark of GMO Global Asset Allocation Series Fund that appears in the Average Annual Total Returns table on page 69 of the Prospectus is amended to "GMO Global Asset Allocation Index."