Biosecurity in the production of broiler chickens is very important but it is hard or even impossible to maintain; hence, promotion of immune responses could control diseases in chickens. At present study, the effect of six levels of oil-extracted propolis (0, 50, 100, 150, 200 and 250 mg/kg ration) on immune system against Newcastle virus was studied using a completely randomized design with 360 chickens. Blood antibody ratio against the Newcastle virus (HI test), the weight of thymus, bursa fabricius and the percentage of lymphocytes were measured for a period of 42 days and the data were analyzed. The results indicated that the rate of antibody has significantly (p<0.05) increased with an increase in the amount of propolis in diets and with the levels of 250 mg/kg ration the antibody rose to 10.42 titre at the age of 42 compare to control (6.42). The weight of thymus gland also increased significantly (p<0.05) with the increase in the levels of propolis and at the levels of 250 mg/kg in ration, weight of thymus increased up to 14.54g in compared to control (8.47 g). Similarly the weight of bursa fabricius significantly increased (p<0.05) from 2.42 g in control to 4.62 g in 250 mg propolis/kg of ration (p<0.05). Intake of 200 and 250 mg propolis/kg of ration has significantly increased the lymphocytes to the levels of 50.18 and 51.25 percent compared to the control (48.93 %), respectively. Results indicate that the efficiency of immune-system for immunizing of broiler chickens against Newcastle virus has been promoted using 50 up to 250 mg of propolis per kg of ration.