7-Acylamido-3-[2-(1-methyl-1H-tetrazol-5-yl) vinyl]-3-cephem-4-carboxylic acids including the 7-methoxy derivatives were prepared by two synthetic methods. The first method involves the reaction of the 3-bromomethylcephalosporin derivative (III) with 5-methylsulfinylemthyl-1-methyl-1H-tetrazole (IV) followed by thermal elimination leading to an olefinic compound (VI). An alternative olefin formation was carried out by utilizing the Wittig reaction of the 3-formylcephalosporin derivative (X). Among the 3-tetrazolylvinylcephalosporin derivatives, the mandelamido derivative (XVa) showed the best in vitro antibacterial activities against gram negative bacteria.