AIM: To set up an assay method for the determination of ecdysterone (EDS) in the root of Achyranthes bidentata Bl. by RP HPLC. METHODS: The EDS was separated on a Hypersil ODS column (200 mm×4 6 mm ID, 5 μm), using acetonitrile — water (1 0∶5 4) as the mobile phase and detected at 243 nm. The flow rate was 1 0 mL·min -1 . Phenol was used as an internal standard. RESULTS: The calibration curve was in good linearity over the range of 28 04～280 40 μg (γ=0 9997). The average recovery was 95 2%. CONCLUSION: The method is simple, fast, sensitive and is suitable for quantitative analysis of EDS in the root of Achyranthes bidentata Bl.
