Abstract: A method based on ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) had been developed for simultaneous determination of 6 kinds of soybean isoflavones in health foods. The soybean isoflavones were ultrasonic extracted from contents of soft capsule with 80% methanol, purified by Florisil cartridge and separated by C₁₈ chromatographic column.0.1% formic acid aqueous solution and acetonitrile were used as mobile phase with the flow rate of 0.3 mL/min, the column temperature was 30℃, and the positive ion mode with multiple reaction monitoring (MRM) was used to detect soybean isoflavones. Experiments results showed that daidzin, glycitin, genistin, daidzein, glycitein and genistein were linear in their respective concentration range. The limits of detection were 10 μg/kg for glycitin and glycitein, 20 μg/kg for daidzin and genistin and 30 μg/kg for daidzein, genistein, respectively. The recoveries ranged from 81.8% to 98.4% with the relative standards deviations of 1.8%~6.7%. The results provided a technical reference for quality control and effective utilization of soybean isoflavones in health food, and had certain theoretical significance and application value.