Bioequivalence study is a scientific and practical method used to compare the quality of a generic drug with a reference product. This study aimed to examine the bioequivalence of two closantel formulations produced with different sources of raw material by a domestic pharmaceutical Company. Due to long half- life of closantel, the study carried out by a parallel method. Thirty sheep were divided into 2 groups of 15 each. In the first group (test group) each sheep received 500 mg bolus of closantel and in the second group (reference group), each sheep received a 500 mg bolus of closantel produced with a raw material from a Belgium Company. Blood samples were collected at 0, 4, 8, 12, 16, 20, 24, 32, 48 and 72 hours after drug administration. An HPLC system was used to determine the amount of closantel in plasma. Pharmacokinetic parameters including area under curve (AUC), Cmax, Tmax, Kel and t1/2 of closantel were determined in each sheep. A t-student test was used to analyze and compare the results. The mean ± SD of Cmax in reference and test groups were 56.38±14.28 µg/ml, 51.44±10.55, respectively. Tmax in reference and test groups were 22.93± 2.81, 23.72± 1.83 h, respectively . AUC (0-72) in reference and test drugs were 2049.1±421.2 and, 1795.1± 421.2, respectively. AUC (0-||•||) in reference and test were 2557.3±621.5 and 2171.1± 80. Kel in reference group was 0.0321± 0.0144 while in test it was 0.0348± 0.0128. t1/2 in reference and test groups were 24.85± 8.34 h and, 22.29± 8.03 h, respectively. In conclusion, the results of this study showed that there was not significant difference between reference and test group, suggesting that two products were bioequivalent.