The effects of mycelium of Cordyceps militaris on the growth, the lipid metabolism, the serum protein levels and the enzyme activities in male rats were studied. Sprague-Dawley rats were given four different types of diets for a succeeding period of five weeks: either a control diet, a control diet supplemented with 2%, 3% or 4% mycelium of Cordyceps militaris (CM) powder. The body weight gain, hepatic weight, feed efficiency ratio and the feed intake of the rats given diets with 2%, 3% or 4% CM were similar to those in rats given the control diet. The concentrations of hepatic total lipid and triglyceride of rats fed the 3% or 4% CM diets were significantly lower than those of rats fed the control diet. But the concentrations of hepatic total cholesterol and phospholipid of rats fed the all CM diets were similar to those of rats fed the control diet. The concentrations of total lipid, total cholesterol, triglyceride phospholipid, and the atherogenic index, and the activities of glutamic oxaloacetic transaminase and lactic dehydrogenase in serum of rats fed the all CM diets were significantly lower than those of rats fed the control diet. No differences were noted in the concentrations of HDL-cholesterol, LDL-cholesterol, total protein, albumin and creatinine, and the activities of glutamic pyruvic transaminase, ${gamma}$ -glutamyltranspeptidase and alkaline phosphatase in the serum among the rats with on all the experimental diets. These results showed that the all CM diets feeding decreased the total cholesterol, the triglyceride, the phopholipid, and the atherogenic index in serum of rats.