Objective: To study the pharmacokinetics of rhein rats were given of Radix et Rhizoma Rhei and Dachengqi Decoction. Method: Radix et Rhizoma Rhei group were given a single dose of Radix et Rhizoma Rhei and Dachengqi Decoction group were given Dachengqi Decoction. The plasma concentration of rhein was measured by HPLC. Diomansil C18 (4.6 mm ×150 mm

5 μm)was used as analytical column. The mobile phase consisted of methanol-water-acetic acid(77∶22∶1)

and the wavelength of detection was set at 428 nm. Plasma concentration-time data were analysted with the 3P97 pharmacokinetic software. Result: The linear ranges of rhein were from 1.0 to 15 mg ·L-1 .The concentration-time curves of rhein were fitted to the two compartment models in rats. The main pharmacokinetic parameters of the concentration-time curves and the maximum plasma concentration were significant difference between the Radix et Rhizoma Rhei groups and Dachengqi Decoction group after administrated the same dosage of rhein in rats (P<0.05). Conclusion: It was decreased the concentration of rhein in plasma when Radix et Rhizoma Rhei compatibility with other chinese medicine in Dachengqi Decoction.