Abstract: A GC-MS method for the analysis of dextromethorphan and its metabolites is described. The urine sample was hydrolyzed with HCl, extracted with diethyl ether and derivatized with MSTFA (N-methyl-N-trimethylsilyltrifluoroacetamide)-MBTFA (N-methyl-bistrifluoroacetamide). Dextromethorphan and its 3 metabolites were detected in urine samples within 2～60 h after administration of the drug. Their structures and the variation of their concentration in urine were determined. The detection limit of dextromethorphan is 10 ng.