Abstract: HPLC-MS/MS was applied to the determination of minoxidil of illegal addition in cosmetics. Saturated sodium chloride solution was added in the sample for salting out and demulsification. The sample solution was extracted ultrasonically for 20 min with acetonitrile. After centrifugation, the supernatant was filtered on 0.22 μm filtering membrane. ACQUITY UPLC^® BEH C₁₈ chromatographic column was used as stationary phase, and the mixture of 0.2% (φ, the same below) acetic acid solution and 0.2% acetic acid methanol solution mixed in different ratios was used as mobile phase in gradient elution. ESI⁺ and multi-reactions monitor mode were adopted in MS/MS. Isotope was used as internal standard. Linearity range of minoxidil were found in the range of 5-500 μg·L^-1 with detection limit (3S/N) of 1 ng·g^-1. On the base of blank sample, test for recovery was made by standard addition method; values of recovery found were in the range of 108%-114%, with RSDs (n=6) of recovery amounts in the range of 1.2%-2.8%.