The effects of Paecilomyes japonica on weight gains, food intakes, food efficiency ratios, serum and hepatic lipid concentrations, serum protein levels and serum enzyme activities, were studied in adult male rats. Sprague-Dawley rats,35 weeks old, were given four different types of diets for a succeeding period of five weeks: either a normal diet (5% corn oil), a control diet (high fat; 5% corn oil + 15% lard), a PF diet (control diet + 3% fruiting body of Paecilomyes japonica), or a PM diet (control diet+.3% mycelium of Paecilomyes japonica). The body weight gains, hepatic weights and food efficiency ratios of rats fed the PF or PM diets were significantly lower than those fed the control diet, but were similar to those fed the normal diet. The concentrations of hepatic total lipids, cholesterol and triglyceric, and serum triglyceride, of rats given the PF or PM diets were significantly lower than those given the control diet. Hut the concentrations of total cholesterol, HDL-cholesterol, LDL-cholesterol and phospholipid in the serum of rats fed the control, PF or PM diets were significantly higher than those fed the normal diet. In the serum of rats fed the PF diet, the HDL-cholesterol/total cholesterol ratio was significantly higher and the atherogenic index was significantly lower than those fed the control diet, while such effect was not observed in rats fed the PM diet. The alkaline phosphatase activity in the serum of rats fed the control and PM diets was more significantly decreased compared to rats fed the PF and normal diet. No differences were noted in the weights of the pancreas, kidney and heart, the serum concentrations of glucose, hemoglobin and albumin, and the activities of GOT, GPT and ${gamma}$-GTP, among the rats on all the experimental diets. In conclusion, the rats fed the PF or PM diets maintained normal body and hepatic weights. Despite of the high intake of fats in the PF and PM diets, the concentrations of hepatic total lipids, cholesterol and triglyceride, and serum triglyceride were decreased.