Squalene synthase catalyzes the reductive dimerization of two molecules of farnesyl diphosphate to form squalene at the final branch point of the cholesterol biosynthetic pathway. Due to the unique position of this enzyme in the pathway, its inhibitors may have advantages as antihypercholesterolemic agents. Therefore, selective inhibitors of squalene synthase do not prevent the formation of the essential branch products of the isoprene pathway, such as dolichol, coenzyme-Q, and prenylated proteins, as might be expected for inhibitors of enzymes earlier in the pathway; for example, lovastatin and mevalotin. The current study reports that CJ90002, a pentagalloylglucose isolated from Paeonia moutan SIM (Paeoniaceae), which is an important Chinese crude drug used in many traditional prescriptions, was a potent inhibitor of rat microsomal squalene synthase, and also a potent inhibitor of cholesterol biosynthesis in vitro. In addition, the intraperitoneal and oral administration of CJ90002 had a significant lowering effect on plasma cholesterol levels in hamsters.