This study was conducted to compare the effects of different illumination programs on the cellular and humoral immune system using 320 one day–old male broilers (Arian 386) in a completely randomized design of 8 replications (10 birds each). The four assayed lighting schedules were comprised of: 1- continuous lighting (control), 2- decrease then sudden increase of lighting, 3- decreasing-gradual increasing lighting and 4- intermittent lighting (1 light: 3 dark periods). Humoral immune responses were assessed following immunization by Sheep Red Blood Cells (SRBC) and Newcastle virus (ND) vaccine. Increase in skin thickness due to Dinitrochlorobenzen (DNCB) contact was utilized to assess the cellular immune response: Total antibody against SRBC was lower in the sudden increase in lighting program as compared with the other programs (P<0.05). During the first immunization treatment the 2-mercaptoethanol resistant anti-SRBC antibody was decreased in the intermittent program as compared with control (P<0.05). The 2-mercaptoethanol sensitive anti-SRBC antibody was significantly lower in gradual as well as in sudden increase programs in comparison with control and intermittent groups (P<0.05). Anti-ND antibody was the highest in gradual increasing group as compared with control and other lighting programs (P<0.05). The skin thickness response to DNCB increased in intermittent and gradual increasing programs compared to control (P<0.05). Heterophil to lymphocyte ratio decreased in all lighting schedules as compared with continuous lighting of control group (P<0.05). Weight of bursa was increased in sudden increasing schedule as compared with control and other lighting programs (P<0.05). It could be concluded that introduction of some limitation in lighting hours is a practical tool for improvement of immune system. The observed results emphasized the application of decreasing-gradual increase lighting program could modulate the cellular as well as and humoral immune responses in Arian broilers.