This study was performed to investigate the effects of liquid culture of Agaricus blazei Murill on the weight gains, food efficiency ratios, serum protein and mineral levels, and serum enzyme activities in growing male rats. Sprague-Dawley rats (7 weeks old) were given four different types of diets for a succeeding period of 6 weeks, respectively: a normal diet group, a control diet group (normal diet + 15％ lard + 0.5％ cholesterol), a 30％ or 40％ A. blazei diet groups (control diet + 30％ or 40％ A. blazei in water) according to the levels of A. blazei supplementation. The body weight gains, food efficiency ratios, and the liver of the rats fed control diet, 30％ or 40％ A. blazei diets were significantly increased compared to rats fed the normal diet, but those of rats fed the 30％ and 40％ A. blazei diets were similar to those of rats fed the control diet. The concentrations of total protein, albumin, glucose, and hematocrit value in serum of rats fed the control diet, 30％ or 40％ A. blazei diets were similar to those of rats fed the normal diet. The concentrations of urea and creatinine in serum of rats fed the 30％ or 40％ A. blazei diets were similar to those of rats fed the control diet. but the urea of rats fed the 30％ and 40％ A. blazei diets were significantly decreased compared to rats fed the normal diet. The concentrations of Ca, P, Fe and Mg, and $Ca^{++}$, $K^+$, $Na^+$ and $Cl^-$ of rats fed the control diet, 30％ or 40％ A. blazei diets were similar to those of rats fed the normal diet. There were no differences in the activities of aspartate aminotransferase, alanine aminotransferase, $gamma$-glutamyltranspeptidase and alkaline phosphatase in the serum among the experimental groups. In conclusion, the rats fed the A. blazei maintained normal protein and mineral levels, and enzyme activities of serum. But the A. blazei feeding could not decrease the body and liver weights in the rats fed high cholesterol diets.