Prodrug of cefazolin (CFZ) was prepared with the objective of improving its oral bioavailability. Cefazolin phthalidyl ester (CFZ-PT) was synthesized and evaluated as potential prodrug form. The successful synthesis of CFZ-PT was identified by spectroscopic analysis. Partition coefficient studies showed that CFZ-PT is more lipophilic than CFZ and the ester was hydrolyzed enzymatically into the parent drug in blood, liver and intestinal homogenates. The pharmacokinetic characteristics of CFZ-PT and CFZ were compared following oral administrations to rabbits. Serum CFZ concentration was determined by HPLC method and the ester compound (prodrug) was not detected in serum following oral administration of CFZ-PT. CFZ-PT did not have antimicrobial activity in vitro against Bacillus subtilis ATCC 6633, whereas CFZ-PT in serum after oral administration to rabbits had antimicrobial activity. From above observations, it was noted that CFZ-PT is rapidly hydrolyzed to CFZ in the body and the bioavailability of CFZ-PT was increased by 3.5-fold than that of CFZ. From these results of this study, it was concluded that CFZ-PT may be a novel prodrug of CFZ which can improve the oral absorption of CFZ.