The Effect of toltrazuril on the disposition kinetics and bioavailability of thiamphenicol following a single intravenous (IV) and oral administrations in broiler chickens at a dose of 30 mg/kg body weight was investigated. The serum thiamphenicol concentration was detected by high performance liquid chromatography. After IV injection, thiamphenicol serum concentration was best to be described by a two-compartment open model. Toltrazuril pretreatment was resulted in a significance increase in Vdss and Cltot (3.51±0.1and 0.38±0.005 L/kg, respectively) of thiamphenicol compared with thiamphenicol administered alone (2.31±0.1 and 0.31±0.006L /kg, respectively).The elimination half-life and the mean residence time of thiamphenicol were 4.58±0.2 and 2.44±0.1, 5.72±0.2 and 2.25±0.1h., in control and toltrazuril pretreated chickens, respectively. Following oral dosing, the maximum serum concentration was 14.58±0.1 and 11.88±0.04 μg/ml reached at 3.64±0.01 and 3.56±0.01h, in control and toltrazuril pretreated chickens, respectively. Oral bioavailability was found to be 117.79± 1.2 and114.85 ±0 .7 % in control and toltrazuril pretreated chickens, respectively. It was concluded that the pretreatment of toltrazuril with thiamphenicol in broilers altered the pharmacokinetic profile of thiamphenicol.