Abstract: The effects of dietary trypsin inhibitor (TI) detected in raw and boiled soybean on the growth of Nile tilapia, Oreochromis niloticus, were studied. The present research demonstrated that hydrothermal treatment not only reduced 81.4% of TI activity in raw soybean, but also significantly increased PER of soybean protein, from 1.12 to 1.76. The Nile tilapia grow well if the levels of dietary trypsin inhibitor are not higher than 0.09%.