Abstract: Objective:To establish the determination method of the serum contents of paeoniflorin and erulic acid in rats treated with intragastric administration of Siwu decoction using high performance liquid chromatography(HPLC).Methods:Twenty-four rats were randomly divided into the control group,low and high dosage of Siwu decoction groups(8 rats each group).The control group,low and high dosage of Siwu decoction groups were treated with intragastric administration of distilled water,0.3 g/mL and 0.6 g/mL Siwu decoction(10 mL/kg) for 7 days.The serum in three groups were harvested from abdominal aorta under chloralic hydras anesthesia,and analyzed using HPLC at the 230 nm of wave length.Results:The linear regression equation,r value and linear range of paeoniflorin and erulic acid were Y=1.019 0X-0.031 & Y=1.026X+0.091,0.999 8 & 0.999 7 and 0.62 to 18.03 μg/mL & 0.32 to 5.11 μg/mL,respectively.The precision,specificity,stability and extraction recovery rate met with the requirement.The serum contents of paeoniflorin and erulic acid in high dosage of Siwu decoction group were significantly higher than those in low dosage of Siwu decoction(P<0.01).Conclusions:This method can determinate the serum levels of paeoniflorin and erulic acid in rats treated with intragastric administration of Siwu decoction.