The objective of this paper is to establish a suitable method for the determination of related substances in cefprozil by RP-HPLC.The C18 column (250 mm × 4.6 mm, 5 μm) and the acetonitrile-phosphate buffers solution (10:90) were used, and the detection wavelength was at 280 nm.The results showed that the resolution between cefprozil and the related substances was ideal.Three batches of samples were tested and the content of the known related substances was 0.14%, 0.15%, and 0.15%, resp.The content of the other maximum individual impurity was 0.38%, 0.39%, and 0.36%, resp. and the total content was 1.20%, 1.15%, and 1.18%, resp.It was concluded that this method is simple, accurate, and may be used to determine the related substances in cefprozil.