Abstract: AIM：To develop a capillary GC method for the indirect determination of CYP2D6 activity. METHODS: After an oral dose of 30 mg dextromethorphan, urine samples were collected and extracted, then analysed on a 0.22 mm×25 m HP-1 column coupled with FID detector. The temperatures of the column, injector and detector were 190℃, 260℃ and 260℃, respectively. RESULTS: Dextromethorphan (DM) and its metabolite dextrorphan (DT) were well separated. There was good linear relationship between chromatographic area and concentration in the concentration range of 0.20～1.60 μg.mL^-1 for DM and 0.40～20.00 μg.mL^-1 for DT. The recoveries of DM and DT were 99.5% and 99.8%, respectively. Within day's relative standard deviations were no more than 5.47% for DM and 6.19% for DT. The lowest detection limits were 8 ng for DM and 4 ng for DT. The CYP2D6 activities in 11 volunteers were determined with this method. CONCLUSION: The established GC method was simpler than previous GC method, it can be used for the determination of CYP2D6 activity.