The (R) -lansoprazole powder for injection was dissolved in methanol to prepare a 5.00 mg·L-1 sample solution, and chromatog. anal. was carried out under the following conditions: Chiralpak ID chiral column (4.6 mm×250 mm, 5μm) was used as stationary phase, the column temperature was 35 °C, the mobile phase was a mixture of n-hexane, isopropanol and glacial acetic acid (70+30+0.2), the flow rate was 0.6 mL·min-1, and the diode array detector was used for detection at the wavelength of 285 nm.The results showed that, linear relationship was found between peak area and mass concentration of (S) -lansoprazole in the range of 0.48-4.81 mg·L-1, the detection limit (3 S/N) was 2.4×10-3 mg·L-1, and the lower limit of determination (10 S/N) was 4.8×10-3 mg·L-1.Values of recovery obtained by standard addition method were in the range of 97.5%-103%, and RSDs (n=6) were less than 1.6%.