Abstract: OBJECTIVE To establish a GC method for the determination of menthol in 5% menthol hydrogel patch. METHODS Firstly, the pretreatment methods of volatile oil extraction and ultrasonic extraction were compared. Sencondly, the content of menthol was determined by GC:using capillary column with polyethylene glycol 20000 as stationary phase (30 m×0.32 m, 0.25 μm); nitrogen as the carrier gas, with column temperature of 140℃, and FID detector as the detector. RESULTS Sample could be well extracted by ultrasonic extraction. The methodological investigation of the detection method of menthol gel patch showed that the RSD of precision was 0.4%, the RSD of repeatability was 0.67%, the average recovery rate was 97.02% with RSD of 0.17%, the linearity was good within the menthol concentration range of 0.175-2.1 mg·mL^-1 and the regression equation was Y=0.802X-0.000 7(r=0.999 9). Then 11 batches of the product samples were determined by the established method, and all the results were qualified. CONCLUSION Because of the influence of the cross-linking and solidity of hydrogel patch, the ultrasonic extraction is more reliable and stable than the volatile oil extraction in pretreatment. The established GC method is reliable, stable and reproducible for the determination of menthol in hydrogel patch. It can be used for the quality control of menthol hydrogel patch.