Abstract: A method of high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was developed for the simultaneous determination of nine banned alkaloids in cosmetics, including strychnine, pilocarpine, veratrine, noscapine, lobeline, atropine, hyoscine, ephedrine and physostigmine. Water was selected as dispersant agent, a mixture of ammonia-methanol (2∶98, V/V) solution was selected as extracting agent, meanwhile, n-hexane was adopted for defat treatment, so the purification and extraction could be accomplished in one step. The chromatographic separation was achieved by using a Poroshell 120 Bonus-RP column in combination with a gradient elution with 0.2% formic acid in water and acetonitrile. The qualitative and quantitative analysis of the nine alkaloids were operated by electrospray ionization at positive ion mode using multiple reaction monitoring (MRM) mode. The mass spectrometric fragmentation rule of the alkaloids was also studied. The results showed that the linear relationships are good corresponding to concentration ranges, and the correlation coefficients are 0.997 8-0.999 8. The limits of detection (LODs) and the limits of quantitation (LOQs) range from 0.03 to 0.36 μg/kg and 0.1 to 1.2 μg/kg, respectively. The recoveries are 85.3%-135.3% at three spiked concentrations, and the relative standard deviations (RSDs) are 1.0%-13.4%. The method is fast, accurate and sensitive, and it is suitable for the detection of the banned alkaloids in cosmetics and the evaluation of the safety of cosmetics.