Abstract: LC-MS/MS was applied to the determination of 6 synthetic cannabinoids in plant sample. The plant sample (20 mg) was extracted ultrasonically with 50 mL of methanol for 30 min. After centrifugation, the supernatant obtained were used for LC-MS/MS determination. C₁₈ chromatographic column was used as stationary phase, and the mixture of methanol and water mixed in different ratios was used as mobile phase in gradient elution. ESI⁺ and multi-reactions monitor mode were adopted in MS/MS. Linear relationships between values of peak area and mass concentration of the 6 synthetic cannabinoids were kept in definite ranges, with detection limits (3S/N) in the range of 0.2-3.0 μg·L^-1. Values of recovery found by standard addition method were in the range of 95.9%-104%, values of intra-day RSD's (n=5) less than 6.5% and inter-day RSD's (n=5) less than 8.0%.