In vitro and in vivo trials, were done to evaluate the antimicrobial activity of ceftiofur sodium as anti-infective chemotherapeutic agent belonged to the third generation cephalosporins against differ-ent bacterial pathogens. The obtained results re-vealed that it was more effective and superior in its action than the other compared antibacterial agents. In disc diffusion test most P. multocida isolates were highly sensitive to ceftiofur sodium with minimum inhibitory concentrations (MICs)ranging between 0.625 - 2.5 (g/ml) and minimal bactericidal concentration (MBCs) equal to or (Two folds of the MICs.