Amino acid 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. The objective of this study was to determine the Tryptophan requirement in EG (d 35 to 53) and LG (92 to 111) using the indicator amino acid oxidation method.  It was found that heat production and energy retention were not affected (P = 0.92) by Trp intake but increased and decreased, respectively from EG to LG. 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.