The effect of salinomycin drug on the immune system of chickens was investigated. By using the recommended dose 60 mg/kg feed salinomycin was given as anticoccidial drug continuously for 49 days. There was no noticeable significant effect on the humoral and cell-mediated immune responses to Newcastle Disease Virus (NDV) Vaccine. A drastic immunosuppressive effect was manifested by using a dose of 120 mg/kg and characterized by lowered titers of antibodies to NDV, decrease in the relative weight of lymphoid organs, lowered mitogenic response of peripheral blood lymphocytes (PBL) to phytohaemagglutinin (PHA) with reduction of heterophils percentage, as well as reduced protection rate to intramuscular challenge with the velogenic viscerotropic (VV) strain of NDV.