A high performance liquid chromatography-tandem mass spectrometric(HPLC-MS/MS) method was established for the determination of bimatoprost in eyelash enhancing cosmetics serums.The samples were extracted with 50%(by vloume) methanol,then separated on an Agilent Poroshell 120 EC-C18(4.6 mm×100 mm,2.7 μm) column by isocratic elution,with 5 mmol·L-1 ammonium acetate containing 0.02% formic acid-acetonitrile(55∶45) as mobile phases at a flow rate of 0.3 mL·min-1.The analyte was detected by HPLC-MS/MS with electrospray ionization source in positive ion mode(ESI+) and multiple reaction monitoring(MRM),and quantified by external standard method.Results showed that there existed a good linear relationship for bimatoprost in the range of 0.50-100 ng·mL-1 with a correlation coefficient(r2) of 0.998 2.The limit of detection(LOD,S/N=3) and limit of quantitation(LOQ,S/N=10) were 0.015 and 0.05 μg·g-1,respectively.The recoveries at low,medium and high spiked levels were 98.6%,101% and 99.2%,with relative standard deviations(RSDs) of 2.4%,2.1% and 1.2%,respectively.The method is simple,rapid and high sensitive,and is suitable for the rapid determination of bimatoprost in eyelash enhancing cosmetics serums.