A high-performance liquid chromatographic method for the determination of cinnamic acid in Cinnamomi ramulus and paeoniflorin in Paeoniae radix was established. The samples were separated by a LiChrospher RP-18 column with water-acetonitrile-methanolacetic acid (61:34:5:0.1 or 80:15:5:0.1, v/v) as the mobile phase at a flow-rate of 1.0 ml/min. Cinnamic acid and paeoniflorin were determined by UV detection at 280 and 250 nm, respectively. The method was applied to determine the optimum conditions for the extraction of the traditional Chinese medicinal preparation Huang Chi Chien Chung Tong, which contains Cinnamomi ramulus and Paeoniae radix. The results indicate that the best extraction conditions involved the use of an ultrasonic bath at 60 degrees C for 30 min. In this experiment, butyl paraben and methyl paraben were used as the internal standards for cinnamic acid and paeoniflorin, respectively. A good and reproducible separation of cinnamic acid and paeoniflorin was obtained within 15 min. The method was also applicable to other preparations that contain Cinnamomi ramulus and Paeoniae radix such as Guey Chi Chia Long Ku Muu Li Tong, Kuei Chi Chien Chung Tong and Tang Kuei Chien Chung Tong.