OBJECT To Study the pharmacokinetics and metabolism of Sodium 7,4' -oxo-acetic acid daidzein in rat. METHOD Sodium 7,4' -oxo-acetic acid daidzein was determined by reversed-phase HPLC (column: German CenturySIL BDS C18 5 μm silica, 200 mm x 4.6 mm i.d; fluid: methanol-water-85% phosphoric acid(57:43:0.05, v/v/v)), with sodium benzoic acid as an internal standard. Biological samples were extracted with acetonitrile. RESULTS The calibration curve was linear over the range of 1.0-1000 μg/ml in rat plasma, urine and feces. The average extraction recoveries were 73.3% (plasma), 73.9% (urine) and 83.7% (feces) respectively and the intra-day and inter-day precisions were less than 8.34%. The assay was applied to the analysis of samples from a pharmacokinetic study. The absolute bioavailability of oral administration was 3.07%. DZ I original compound determined in 6h urine was 32.32%, in 24h urine was 32.71%, in 24h feces was 22.96%.