Pleurotus citrinopileatus is a popular edible mushroom which is physiologically active in both humans and animals. In the study we investigate the effects of this mushroom on hyperlipidemic hamster rats. Four dietary forms of the mushroom were created as follows. The powdered dry fruiting body, hot-water extract, and two kinds of elutes were obtained, from ethyl acetate extract and methanol extract, respectively, in different mixed proportion solvents over silica gel column chromatography (referred to as EAE and MOE, respectively). They were tested at different dosages as a supplement to a high-fat diet in hyperlipidemic rats. Serum triglycerides and total cholesterol levels were significantly lower in groups supplemented with the highest dosages of EAE and MOE (0.5 g/kg, body weight daily) as compared with the control groups that received no mushroom additive. High-density lipoprotein levels in these same two experimental groups were also significantly higher than those in the negative control group. The tested rats that were fed with EAE had the highest serum glutathione peroxidase and superoxide dismutase activity, and those with the MOE and EAE had the highest DPPH free radical scavenging activities and ferric-reducing abilities, tested in vitro. The major constituents of MOE and EAE were identified as ergosterol and nicotinic acid, respectively. P. citrinopileatus extracts may have a significant antihyperlipidemia effect. Furthermore, antioxidant activities and antihyperlipidemic effects of MOE and EAE seemed to display similar tendencies.