To establish a HPLC method for the determination of diosmin in Rats plasma and to study the pharmacokinetics of diosmin in Rats.Rats were given diosmin with 3 doses as 225, 325, 425 mg x kg(-1). Blood samples were collected at different times after oral administration. The plasma concentration of diosmin was determined by HPLC, and the pharmacokinetics parameters were calculated by 3p97 program.The typical equation of diosmin in rats plasma was Y = 3.05 x 10(-3) C + 1.55 x 10(-3), the calibration curves of diosmin was linear in the range from 0.5-100 microg x mL(-1) (R =0. 996 4). The lowest concentration of diosmin in plasma was 0. 2 g x mL(-1). Its recoveries was more than 85%, and the interday and intraday precision, which was expressed as RSD, were all less than 15%. After 3 doses oral administration of diosmin in rats, the mean plasma concentration-time curves were found to fit one compartment model, and the main pharmacokinetics parameters were obtained.It is first time to establish the HPLC method to determine the concentration of diosmin in rats plasma, and the method described in this report has high sensitivity and selectivity, and it was suitable for pharmacokinetics studies of diosmin. The internal process of diosmin in rats is fit to one compartment model.