Curcumin specifically exhibits cytostatic and cytotoxic effects against tumors of multiple origin. Previously we have demonstrated apoptotic activity of curcumin against tumor cells with no effect on normal cells in-vitro. Many anti-cancer drugs exhibit deleterious effects on immune cells, which restrict their wide use in-vivo. In the present study, we have evaluated the effect of curcumin on the major functions of T cells, natural killer cells, macrophages and on total splenocytes in-vivo, which insight the role of curcumin on their broad effector functions. This study demonstrates that prolonged curcumin-injections (i.p.) do not impair the cytotoxic function of natural killer cells, the generation of reactive oxygen species and nitric oxide from macrophages and the levels of Th1 regulatory cytokines remained unaltered. Interestingly, curcumin-injections enhanced the mitogen and antigen induced proliferation potential of T cells. We have also evaluated immunomodulatory effects of curcumin in ascites-bearing animals. This study strengthens our belief that curcumin is a safe and useful immunomodulator for the immune system.