NOVELTY - Removal of sodium 2-mercaptobenzothiazole impurity comprises reacting (g) a flomoxef intermediate or 7-aminocephalosporanic acid (7-aca) (100), active side chain ester (110-230), 1300-1700 mL organic solvent, and 80-100 mL triethylamine for 3-10 hours at 5-15 degrees C; pouring the material liquid in 1600-3000 mL water, adjusting pH value by hydrochloric acid, separating out yellow solid impurity 2-mercaptobenzothiazole, stirring, filtering, washing the impurity by water, and decoloring the filtrate by activated carbon; and separating out the solid, crystallizing, filtering, washing, and drying.    USE - Method for the removal of sodium 2-mercaptobenzothiazole impurity (claimed).    ADVANTAGE - The method is environment-friendly.    DETAILED DESCRIPTION - Removal of sodium 2-mercaptobenzothiazole impurity comprises:    (A) reacting (g) a flomoxef intermediate or 7-aca (100), active side chain ester (110-230), 1300-1700 mL organic solvent, and 80-100 mL triethylamine for 3-10 hours at 5-15 degrees C;    (B) pouring the material liquid in 1600-3000 mL water, adjusting pH value to neutral by hydrochloric acid, separating out yellow solid impurity 2-mercaptobenzothiazole, stirring for 1 hour, filtering, washing the impurity by 600 mL water, decoloring the filtrate containing the product by activated carbon, and adjusting the pH value to 2.5-2.9 by hydrochloric acid; and    (C) separating out the solid, crystallizing for 1 hour, filtering, washing, and drying.    The corresponding flomoxef intermediate is (7-amino-3-(triazanaphthalene flunarizine) thiomethyl-4-cephalosporanic acid) and (7-amino-3-vinyl-cephalosporanic acid). The active side chain ester is (2-methoxyimino-2-(2-amino-4-thiazol-yl)-(Z)-thioacetic acid benzothiazole ester), (2-(Z)-(2-aminothiazol-4-yl)-2-acetoxyiminoacetic acid 2-benzothiazole thioester), or ((Z)-2-(2-aminothiazol-4-yl)-2-methoxycarbonyl methoxyimino thioacetic acid-2-benzothiazole thioester). The organic solvent is acetonitrile, ethanol, tetrahydrofuran, acetone, or methanol.