The synthesis of the target compound was achieved (91.49% yield) 6-aminopenicillanic acid (6-APA) and an acid anhydride as starting materials and the product thus obtained was confirmed by elemental anal., IR, 1H-NMR, 13C-NMR and final product quality measured up to CP2005. In conclusion, compared with a previously reported process, problems associated with a reaction of mixed acid anhydrides and hydrolysis were solved. The improved process had high yield, low cost and was easy to operate, while the product quality was very high.