BACKGROUND: in this experiment, the effect of consecutive oral levamisole usage on cellular and humoral responses of broilers immune system was evaluated. OBJECTIVES: The aim of this experiment was to determine the best level of levamisole for stimulating immune system of broilers. METHODS: The experiment was conducted by 250 day old (male and female) broiler (Ross) chicks with an average live weight of 40.2g. Effect of zero (control L0), 3.5 (L3.5), 7 (L7), 14 (L14) and 28 (L28) mg/l of levamisole in drinking water from 5 to 25 days under randomized design using a factorial experiment with 5 replication were studied. Cellular immune responses were assayed by PHA-P injection in the skin fold of wings (day 15) and thickness of skin were measured after 24 and 48 hours. Sheep Red Blood Cell (SRBC) 25% were injected in the breast muscle in days 7 and 21 to investigate humoral immune responses, and IgG titer against SRBC was determined in days 7, 14, 28, 35, and 42 by agglutination test. RESULTS: Cellular immune responses to PHA-P in treatments containing 7 and 14 mg/l of levamisole (0.272 and 0.205, respectively) were significantly affected (p<0.05). IgG titer against SRBC in treatment containing 14 mg/l of levamisole (6.16) was significantly higher than other groups (p<0.05). Carcass trait of broiler chicks were not affected by different level of consecutive oral levamisole (p>0.05). CONCULUSIONS: The low level (up to 14 mg/L) of consecutive oral levamisole promotes cellular and humoral immune system responses of broiler chicks.