Polychlorinated biphenyls (PCBs) are synthetic organic compounds with two phenyl groups well known environmental pollutants. This study examined the effect of persistent exposure to 2,3',4,4',5-pentachlorobiphenyl (PCB118) on serum cholesterol levels in male rats. Male Sprague Dawley rats were administered weekly intraperitoneal injections of either PCB118 (20 mg/kg) dissolved in corn oil or corn oil alone. One week after 2 and 5 administrations, the rats were sacrificed by a pentobarbital injection, and the effect of PCB118 on the serum levels of total cholesterol, high density lipoprotein-cholesterol (HDL-cholesterol), and low density lipoprotein-cholesterol (LDL-cholesterol) was investigated. The protein expression level of apolipoprotein A-I (apo A-I) and 3-hydroxy-3-methylgulutaryl coenzyme A (HMG-CoA) reductase was also examined. In this study, the administration of PCB118 induced hyperalphacholesterolemia in rats. In addition, the protein expression level of HMG-CoA reductase and apo A-I was higher in the PCB118-treated rats than in the control. These results suggest that the hyperalphacholesterolemia induced by PCB118 in male rats may be associated with an increase in HMG-CoA reductase and apo A-I expression.