Objective To establish a RP-HPLC method for determining paeoniflorin in Tongtian oral liquid. Methods The content of paeoniflorin in Tongtian oral liquid was determined by RP-HPLC. Kromasil C18 column（4.6 mm?50 mm，5 μm）was used,wity a mobile phase of A(acetonitrile)-B(0.1% phosphoric acid),and with a gradient elution.The column temperature was 30℃,the detection wavelength was 230nm,and the injection volumn was 10礚. Results The linear range of paeoniflorin was 0.339礸/mL-3.782礸/mL, r=0.9999. The average recovery of paeoniflorin was 98.75% （RSD=1.85%，n=9）. Conclusion The quantitative method is simple,feasible and reproducible,and can be used for quality control of Tongtian oral liquid.