Abstract: A method was proposed for simultaneous determination of 13 α-hydroxy acids in cosmetics by ultra-high performance liquid chromatography triple quadrupole mass spectrometry (UHPLC-MS/MS). The sample(0.2 g) was extracted for 30 min in water by ultrasonic, while the undispersed samples added isopropanol firstly. After centrifuging and filtering, the extracted solution was analyzed by UHPLC-MS/MS. The saparation of 13 target compounds was performed on a Agilent Zorbax RRHD SB-Aq C₁₈ column, using mixtures of 0.1% (volume fraction) formic acid solution and acetonitrile at different volume ratios as mobile phases for gradient elution. Electrospray ion (ESI) source with multiple reaction monitoring (MRM) mode in the negative ion mode were adopted in MS analysis. As shown by the results, linear relationships between values of peak area and mass concentration of 13 α-hydroxy acids were found in definite ranges, with detection limits (3S/N) of 0.030 μg·g^-1 for hydroxycaprylic acid, benzilic acid, and α-hydroxy-decanoic acid, 3.0 μg·g^-1 for glycolic acid and lactic acid, and 0.30 μg·g^-1 for the other 8 α-hydroxy acids. Test for recovery was made by standard addition method, giving results in the range of 85.1%-114%, with RSDs (n=6) of the determined values less than 10%. This method was applied to the analysis of 20 samples, with the total amounts of α-hydroxy acids in the range of 20-6 800 mg/100 g, which were all in standard permission scope except an exceeding sample.