Abstract: A 4×2 (Cu×V_A) random experiment was designed to investigate the effect of different dietary levels of Cu (0 mg·kg^-1, 8 mg·kg^-1, 150 mg·kg^-1, 225 mg·kg^-1) and V_A (1 500 IU·kg^-1, 5 000 IU·kg^-1) on broiler immune system at 0~4 and 5~7 week-old. The results showed significant effects (P<0.05, P<0.01) of Cu at 8 mg·kg^-1 on percentage of activated T-lymphocytes in spleen and serum antibody titers of 0~4 week-old broilers. At the same Cu level, percentage of activated T-lymphocytes in spleen, thymus and cecal tonsil, and percentage of activated B/T-lymphocytes in peripheral blood significantly increased (P<0.05, P<0.01) in 5~7 week-old broilers. Percentage of activated B/T-lymphocytes decreased at different degrees under high Cu levels of 150~225 mg·kg^-1 feed. At V_A supplemental level of 5 000 IU·kg^-1 feed, percentage of activated T-lymphocytes in peripheral blood also significantly increased (P<0.05) for the 0~4 week-old broilers, while percentage of activated T-lymphocytes in spleen, cecal tonsil and serum antibody titers significantly increased (P<0.05, P<0.01) for the 5~7 week-ld broilers. Percentage of activated B/T-lymphocytes and serum antibody titers were not significantly affected by Cu/V_A interaction for 0~4 week-old broilers. However, percentage of activated T-lymphocytes of cecal tonsil, thymus and peripheral blood significantly increased (P<0.05) for 5~7 week-old broilers, especially under Cu (8 mg·kg^-1) × V_A (5 000 IU·kg^-1) interaction. Cu/V_A interaction had a significant effect on the function of broiler immune system.