Abstract: High performance liquid chromatography was employed for the quantitative determination of intermediate of cefazolin, 7-amino-3-(2-(5-methyl-1, 3, 4, thiadiazolyl) thiomethyl)- △3 cephem-4-carboxylic acid which is so called as "cleavage product". Good assay result can be obtained by using external standardization or standard addition method, on YWG-NH2 column with 0.6M acetate buffer solution as mobil phase and UV detector (at 272nrn). The average relative deviation of these two methods is 3%. The proposed method is suitable for the quality control in the process of manufacture of cefazolin.