Amino acid (AA) requirements of sows may change from early (EG) to late (LG) gestation due to the accelerated growth of products of conceptus after d 70 of pregnancy. Because Tryptophan (Trp) is a co-limiting AA in corn-soy diets, this study was conducted to determine the Trp requirement in EG and LG using the indicator AA oxidation method.  It was found that the changes in Trp requirement and energy retention during gestation cannot be adequately met by increasing the feed allowance of a single diet throughout pregnancy. Therefore, phase feeding of 2 diets with different Trp contents is necessary to balance Trp and energy intake with the changing Trp and energy requirements in pregnancy.