Abstract: OBJECTIVE To evaluate the protein content in Xinmailong injection. METHODS The protein content in Xinmailong injection was measured by Bradford assay connected with standard addition method of second derivative spectrum method to exclude interference. RESULTS The present study was conducted to elucidate that the protein content of about 0.15 mg·mL^-1 present in Xinmailong injection and a common standard curve to detect the content present in protein by standard addition methods of second derivative spectrum method was established. CONCLUSION The protein content in Xinmailong injection could be evaluate accurately by the method of Bradford assay connected with standard addition method of second derivative spectrum method.