A high performance liquid chromatog. coupled with pre-column derivatization method was developed for determining di-Me sulfate (DMS) in synthetic paeonol samples.The synthetic paeonol samples reacted with p-nitrophenol under alk. and heating conditions and synthesized p-nitroanisole, which was determined by HPLC-UV detector, with C18 (250 mm×4.6 mm, 5 μm) as column.The conversion rate of this derivatization was stable and durable.The solvent blank and paeonol samples did not interfere with the determination of DMS.The linear range appeared from 0.122 to 1.120 mg·L-1.The detection limit was 0.82 ng.The precision measured by relative standard deviation (RSD) of peak area for the standard solution was 1.69% (n=6) for intra-day detection and 1.89% (n=12) for inter-day detection, resp.The average recovery was 98.8% (RSD=1.40%, n=9).The method is applicable, specific, and accurate for the determination of DMS in synthetic paeonol samples.