The pharmacokinetics of ceftiofur was studied following intravenous and intramuscular (single & repeated) administrations. Following a single intravenous injection of 10 mg/kg body weight of ceftiofur in normal chickens, serum concentration-time curve was best described by a two compartments open model with elimination half life (t0.5(β) = 5.47 hour), volume of distribution (Vdss=198.60 ml/kg) and total clearance of the drug (CLtot= 0.345 ml/kg/min). Following a single intramuscular administration of 10 mg/kg. body weight ceftiofur in normal chickens, The peak serum concentration (Cmax) was 25.94 µg/ml was achieved at a maximum time (Tmax) of 2.51 hour. The mean systemic bioavailability was 88.90%. The serum concentrations of ceftiofur following repeated intramuscular administration of 10 mg/kg body weight once daily for five consecutive days in normal and experimentally Escherichia coli infected chickens showed a lower significant values recorded in experimentally Escherichia coli infected chickens than in normal ones. Ceftiofur showed accumulative behavior in serum of chickens. Results of this study indicated that ceftiofur was useful for treatment of Escherichia coli infections in chickens. Ceftiofur was assayed in serum, heart, liver, spleen, kidney, fat, breast muscle, thigh muscle and skin after 24, 48, 72, 96 and 120 hours post last dose following administration of 10 mg/kg body weight every 24 hours.