Abstract: In this paper, a novel and simple RP-HPLC method for the determination of related substances of tiopronin for injection was described. The RP-HPLC analysis was performed on a C₁₈ column, with acetonitrile-0. 1% phosphoric acid(8 ∶92), mobile phase in isocratic mode at a rate of 1. 0 mL/min. The photodiode array detector was set at 210 nm. Seven related substances were detected and the structures were characterized by mass spectrometry. The method showed great suitability, specificity and excellent linearity over the concentration range of 0. 3 to 50 μg/mL(r≥0. 999), and the limits of detection and quantitation were found to be 0. 10 and 0. 31 μg/mL, respectively. The accuracy of the method determined by the entire mean recovery ranged from 98. 7% to 103. 7%. The intra-and inter-day precision was satisfactory(RSD≤4. 4%)and robust(RSD≤6. 4%). And this method was successfully applied for the determination of related substances of tiopronin for injection, which revealed the retention of sulfhydryl compounds and glycine analogues on the RP-HPLC and the effect of the pH value of the mobile phase on the chromatographic behavior of the analytes.