Abstract: The mixed internal standard solution (4 mg·L^-1, 0.01 mL), β-glucuronidase solution not less than 850 U·mL^-1 and 0.5 mL of 1 mol·L^-1 ammonium acetate solution were added into 2 mL of the urine sample. After shaking fully, the mixture was hydrolyzed at 37℃ for 2.0 h. After cooling to the room temperature, the volume of the solution was made up to 5 mL with acetonitrile. The solution was froze for 2 h, warmed to the room temperature, and filtered through 0.22 μm organic filter membrane. The 12 metabolites of phthalates in the above solution were determined by high performance liquid chromatography-tandem mass spectrometry, using matrix matching method to eliminate the matrix interference, and internal standard method to quantify. As shown by the results, the linear ranges of working curves of 12 metabolites of phthalates were all 1.00-200 μg·L^-1, with detection limits (3S/N) in the range of 0.05-1.88 μg·L^-1. Test for recovery was made by standard addition method, giving results in the range of 75.3%-114%, with RSDs (n=6) of the determined values in the range of 1.5%-10%. This method was applied to determination of 35 children urine samples, of which 11 metabolites of phthalates were detected, and monoisodecyl phthalate (MDP) was not detected.