9 New cephalosporin derivatives were synthesized and screened for antibacterial activities against various bacteria. (6R,7R) -7$eta$-[(Z)-2-(5-amino-1,2,4-thiadiazol-3-yl)-2-(fluoromethoxyimino)acetamido]-3-[(2-hydroxycarbamoyl)-s-triazolo[1,5-a]-pyrimidin-7-yl]thiomethyl]-3-cephem-4-carboxylic acid sodium salt (compound 3) showed 2 fold enhanced in vitro activity against P. aerurginosa, compared to ceftazidime.