To develop new cephalosporin antibiotics with improved antibacterial activities, a series of 7$eta$-[2-(2-aminothiazol-4-y)-(Z)-2-(1-carboxy-1-methylethoxyimino)acetamido] -3-[5-(heterocycle)thiomethylpy-rrolidin-3-ylthio]methyl-3-cephem-4-carboxylic acid (14~18) having aminothiazol carboxymethylethoxy-imino group on the C-7 position and (heterocycle) thiomethyl pyrrolidinthiomethyl group on the C-3 position of the cephem ring were synthesized. These compounds were tested for antimicrobial activity in vitro against Gram(+) and Gram(-) bacteria. Compounds 15 and 16 showed remarkable antibacterial activity against Salmonella typhimurium TV119 and Alcalienes faecalis KCTC1004, but most of compounds showed lower activity than cefotaxime.