Abstract: Samples (0.25 g) were taken, and 30 mL of methanol was added. The mixture was extracted by ultrasound for 30 min, diluted to 50 mL with methanol, and filtered through a 0.22 μm organic filter membrane, and the subsequent filtrate was introduced into high performance liquid phase chromatography-tandem mass spectrometer. Methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, isopropyl 4-hydroxybenzoate, butyl 4-hydroxybenzoate, isobutyl 4-hydroxybenzoate, pentyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, and benzyl 4-hydroxybenzoate of the 9 p-hydroxybenzoic acid ester preservatives were separated on Waters ACQUITY UPLC^ BEH C₁₈ column by gradient elution with mixed solutions of 0.1% (volume fraction) formic acid solution and acetonitrile at different volume ratios, and detected in negative ion mode of electric spray ion source and multiple reaction monitoring mode. It was shown that mass concentrations of the 9 targets were linearly related with response values in the ranges of 0.5-200.0 μg·L^-1, and detection limits ranged from 0.015 μg·g^-1 to 0.092 μg·g^-1. Test for recovery was made on blank samples by standard addition method, giving recoveries in the range of 88.6%-106%, and RSDs of the determined values (n=6) ranged from 0.90% to 11%. After adjusting the detection instrument, column, mobile phase ratio and column temperature, the 9 targets were well separated, which indicated that the method had a good durability. The proposed method was applied to the analysis of 15 batches of different cosmetic products, and methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate and benzyl 4-hydroxybenzoate were detected. Benzyl 4-hydroxybenzoate with detection amounts of 0.104-0.125 μg·g^-1 was a prokibited perservative, which might be introduced by raw material residues, and detection amounts of the other targets were not more than limits specified by Safety and Technical Standards for Cosmetics (2015 edition).