Abstract: HPLC was applied to the determination of rhein (or called rheinic acid).The Waters symmetry C18 (150 mm×4.6 mm,5 μm) was used as the stationary phase,and a mixed solution of methanol,water and acetic acid in the ratio of 70 to 30 to 2 (by volume) was used as the mobile phase.UV-detection at the wavelength of 254 nm was used.The flow-rate of mobile phase was 0.8 mL·min-1.Precision tests of within-day and between-days repeatability,and of reproducibility in the same laboratory were performed,and RSD′s (n=6) of repeatability obtained were in the range of 0.6%-0.8% and RSD (n=6) of reproducibility was 0.7%.Recovery were tested at 3 different concentration levels giving values in the range of 99.4%-100.2%.In the determination of rheinic acid in its raw material (palmate leaf chinese rhubarb) and products,0.58% of rheinic acid was found in the raw material,and contents of rheinic acid in the products were in the range of 73.1%-90.4%.