GIFT tilapia[initial weight(64.4±1.5)g]were fed purified diets containing six levels(0.08, 0.57, 1.13, 2.09, 4.11 and 8.09 mg/kg diet, respectively)of thiamin for 12 weeks.The experiment was used to determine the dietary thiamin requirement of GIFT tilapia on the basis of growth parameters, hepatic thiamin saturation and a thiamin-dependent biochemical function.The results showed that, with the increasing dietary thiamin level, weight gain rate of tilapia first increased linearly then remained nearly unchanged.Hepatic thiamin contents presented the same tendency with weight gain rate.Fish fed diets supplemented with VB₁ showed significantly higher hepatic transketolase expression, serum high density lipoprotein cholesterol and lower serum pyruvate than fish fed diets without supplementation of VB₁(P<0.05).Fish fed the control diet without supplementation of thiamin showed significantly higher serum pyruvate content than fish fed diets supplemented with thiamin(P<0.05), while protein, moisture, ash, lipid ontent in whole body had no significant differences among various treatments(P>0.05).Based on broken method of the relationships between weight gain rate, hepatic thiamin contents and dietary VB₁ concentrations, it can be concluded that the dietary VB₁ requirement for GIFT tilapia was considered to be 1.16 and 2.06 mg/kg diet respectively.