A new cephalosporin derivative, cefoperazone phthalidyl ester, were synthesized and investigated in terms of dissolution and absorption properties. In comparison with cefoperazone, its phthalidyl ester showed the following characteristics. The mean dissolution time and variance of retention time were more significantly prolonged in simulated intestinal fluid than those in simulated gastric fluid. After a single oral dosing of both cefoperazone and its ester to rabbits, serum concentrations of cefoperazone were measured by bioassay, and the results showed that the ester exhibited much higher and more sustained blood level than the parent drug. The total area under the curve of cefoperazone phthalidyl ester were 10.8 times greater than that of cefoperazone.