The effect of type II synthetic pyrethroid, cypermethrin on selected physiological and biochemical parameters of liver and neural system were studied in male Somali sheep. In addition, the residue of cypermethrin in different tissues and body execreta were also evaluated. Two tested doses (6 and 12 mg /kg b.wt/day) of cypermethrin were given orally to sheep for 63 consecutive days. A vehicle-control group of sheep given corn oil (0.1 ml/kg/day) only was used for comparison. Investigated animals of all groups were slaughtered 24 h after the last dose. No fatality was recorded during the course of this study. Cypermethrin produced significant increase in the weights of liver and spleen, while there were no effects on the weights of brain, kidneys, heart and testes. A significant increase in liver aspartate amino transaminase (AST) and alanine amino transaminase (ALT) activities and a significant decrease in liver lactate dehydrogenase (LDH) activity were recorded in the pesticide-treated animals. Significant decreases were observed in brain Na+, K+-ATPase and Mg++-ATPase in cypermethrin-treated animals that were dose-dependant. Residue analysis revealed higher levels of cypermethrin in spleen, kidneys and muscle than liver. Residues of tested pesticide were detected in all samples of urine and faeces of treated sheep, and were dose-dependent.  From this study it can be concluded that exposure of farm animals for long periods to cypermethrin pesticide will affect their physiological and biochemical parameters with subsequent adverse effect on animal health and production. Moreover, the presence of large amount of tissue residues of this compound in animal tissues and excreta could affect human health as well. Therefore, farm animals should not exposed to theses pesticide for long times via food or water.