Abstract: A series of new 7-(1, 7-disubstituted-l, 4-dihydro-4-oxo-1, 8-naphthyridine-3-carboxamido)—cephalosporins has been prepared by acylation of the 7-amino group of 7-ADCA, 7-ACA, 7-ACT and 7-ACD with 1, 7-disubstituted-1, 4-dihydro-4-oxo-1,8-naphthyridine-3-carboxylic acid. Mixed carboxylic-carbonic anhydride method was adopted in the reactions. Isolation and purification were fulfilled with Sephadex LH-20 column chromatography and centrifugal-TLC technigue. Twenty four new cephalosporin derivatives were synthesized. Their structures have been confirmed by elemental analysis, IR and ¹HNMR. In preliminary In vitro antibacterial sensitivity tests, most of these new derivatives were found to show good sensitivity to Gram-positive bacteria. Bacteriostasis were also observed for some Gram-negative bacteria.