To evaluate the effect of supplemental vitamin C (VC) levels on performance and immune response of broiler chicks, 300 day-old Ross male broiler chicks were allocated to a completly randomized design of 5 treatments(500 and 1000 ppm in diet, 500 and 1000 ppm in drinking water and control). Immunity was assessed as antibody production against Infectious Bronchitis Virus (IBV) and Newcastle Disease Virus (NDV), mitogenic response to PhytohemagglutininA (PHA) and concanavalin A (conA), Cutaneous Basophil Hypersensitivity (CBH) to PHA. Vitamin C ( 500 and 1000 ppm in drinking water and 1000 ppm in diets) increased (P<0.05) daily weight gain (0-21). Maximum body weight gain (42d), daily weight gain(21-42d) and minimum feed conversion ratio were obtained in chicks drinking supplemental 1000 ppm VC. Mitogenic responses were improved (P<0.05) through supplemental 1000 ppm soluble VC for PHA in pure lymphocyte and in whole blood . CBH to PHA was significantly increased (P<0.05) in chickens drinking 500 and 1000 ppm VC. Lymphoid organ weights were not influenced by VC. Humoral immunologic response showed that antibody titer to NDV(HI) and IBV(Elisa) were highest (P<0.05) in groups receiving 500 and 1000 ppm VC in drinking water. All in all the results of the experiment showed that VC administered in drinking water, improved some performance parameters as well as immune response in broiler chicks, specially in early stages of age.