A simple high-performance liquid chromatographic (HPLC) assay using the internal standard method is developed for the simultaneous determination of eight polyphenols. The analyzed compounds isolated from the leaves of Crataegus pinnatifida Bge. var. major include chlorogenic acid, vitexin-4"-O-glucoside, vitexin-2"-O-rhamnoside, vitexin, rutin, hyperoside, isoquercitrin, and quercetin. HPLC analysis is performed on a Diamonsil C18 analytical column (150 x 4.6 mm, i.d., 5-microm) using solvent (A) acetonitrile-tetrahydrofuran (95:5, v/v) and (B) 1% aqueous phosphoric acid as the mobile phase with UV absorption at 270 nm. The calibration curves of the eight polyphenols are linear (r(2) > 0.9992) over the concentration range of 0.0894-120.0 microg/mL. The mean recoveries are 95.4% to 98.1%. The results indicate that the HPLC method developed can easily be applied to the determination of eight polyphenols in the leaves of Crataegus pinnatifida Bge. var. major.