Da-Cheng-Qi decoction (DCQD) is a purgative compound prescription used in China and East Asia. In this paper, pharmacokinetic differences of six major active components (rhein, emodin, aloe-emodin, magnolol, naringenin and hesperetin) between DCQD and its three constitutional herbal medicines, i.e., Radix et Rhizoma Rhei, Cortex Magnoliae officinalis and Fructus Aurantii Immaturus were investigated in rats after oral administration. Plasma samples were analyzed for the quantification of the six active components using validated LC-MS/MS methods. Unpaired Student's t-test was used for statistical comparison. Significant differences (p < 0.05) in the main pharmacokinetic parameters for rhein, emodin, aloeemodin, magnolol, naringenin and hesperetin were found between DCQD and the decoction of its constitutional single herbal medicines, which demonstrated the presence of drug-drug interactions between these constitutional raw materials of DCQD occurring either in the procedure of decoction or during ADME process.