A new method was developed for the simultaneous determination of four nitroimidazoles，e.g.metronidazole(MNZ),ornidazole(ONZ),ronidazole(RNZ) and secnidazole(SNZ), in acne cosmetics by gas chromatography-mass spectrometry(GC-MS).The samples were firstly diluted with sodium carbonate solution and then extracted with ethyl acetate.The extract was subsequently concentrated and/or the fat in which was wiped off with n-hexane.Finally,four nitroimidazoles were derivatised using N,O-bis(trimethylsilyl)-acetamide as derivating agent,and separated on a DB-5 MS capillary chromatographic column(30 m × 0.25 mm × 0.25 μm).The target compounds were identified by GC-MS with retention time and ratio of the characteristic ions under selected ion monitoring(SIM) mode,and quantified by the internal standard method.The result indicated that 4 analytes had good linear relationships(r2≥0.998) in the concentrations of 0.10-5.0 mg/L.The detection limits of target compounds for this method(LODs,S/N=3) ranged from 0.05 mg/kg to 0.10 mg/kg.The recoveries of four nitroimidazoles at three spiked levels in acne cream and acne water samples were in the range of 85.6%-104%,with relative standard deviations(RSDs,n= 6) of 2.9%-6.5%.The real sample analysis showed that this accurate and precise method could be applied in the simultaneous determination of four nitroimidazoles in acne cosmetics.