The present study was conducted to evaluate the comparative effect of soybean protein and casein on body fat deposition in chicks. Chicks were fed an 18% protein diet (soybean protein or casein), and the effects of dietary protein type on growth performance, the lipid contents of the plasma and liver, and the concentrations of plasma glucose and corticosterone were examined. There was no differences in final body weight, and the concentrations of plasma glucose and free fatty acids between the two dietary groups. Hepatic triacylglycerol content and plasma triacylglycerol level, however, were significantly lower in the soybean protein-fed than in the casein-fed chicks. The abdominal fat weight and the plasma corticosterone concentration were markedly lower in the soybean protein-fed chicks. The results suggest that soybean protein in the diet has the effect of lowering the body fat deposition as compared with casein.