To establish an RP-HPLC method for determination of diosgenin in Dioscoreae spp. for quality assessment index in Sub-project 3. The process of simultaneous ultrasonic extraction and hydrolysis for the recovery of diosgenin from Yam was optimized by different pre-processing tests. To accurately determinating the diosgenin, the glycosyl groups on the saponins, both spirostanol and furostanol glycosides, shall be removed by acid hydrolysis and converted to diosgenin (aglycone) before HPLC. The samples were analyzed by HPLC on a Lichrospher 100 RP-18e column and detected at 203 nm with acetonitrile water (90: 10, v/v) as the mobile phase at a flow rate of 1.0 mL/min. The regression equations of diosgenin was Y = 0.0515X-9.277 (r = 0.9916). The intraday and interday relative standard deviations of diosgenin were at the levels of 1.39-3.54% and 2.05-4.77%, respectively. The recoveries of diosgenin added in yam were between 64.2% and 72.0%. The method was applied to three yams grown in Taiwan (D. japonica Thunb. var. pseudojaponica (Hayata) Yamamoto, D. batatas Dence. and D. doryophora Hance), diosgenin was detected in two samples, measurable at 1.04-23.1 mg/g. It was found that the cortex of D. japonica yam tuber contained 4.6?2.1 mg/g which was the highest amount comparison with different parts of yam.