$7{eta}$-[4-Phenyl-5-(3.4.5-trimethoxyphenyl)-4H-1.2.4-triazol-3-yl]thioacetoamidocepharosporanic acid was synthesized by condensation of 7-Aminocephalosporanic acid (7-ACA) with [4-Phenyl-5-(3.4.5-trimethoxyphenyl)-4H-1.2.4-triazol-3-yl] thioacetylchloride. This compound was tested for antimicrobial activity in vitro against nine species of microorganisms. It showed remakable antibacterial activity against Bacillus subtilis, Micrococcus luteus, and Staphylococcus aureus.