Natural flavonoid chrysin was isolated from Indigofera tinctoria leaves and in vitro immunomodulatory effect was evaluated on murine macrophages (RAW 264.7 cell line). Initially the proliferation and phagocytosis effect of different concentrations of chrysin (25, 50 and 100 mu g/mL) was analyzed on normal macrophages. Further the immunomodulatory effect of chrysin was evaluated on LPS (10 mu g/mL) stimulated macrophages with different assays including ROS generation, gene expression and NF-kappa B nuclear translocation. The results revealed that, chrysin significantly increased the proliferation as well as phagocytic function of macrophages in dose dependent manner. On the other hand, chrysin has significantly debited the ROS generation, NO production and increased the arginase activity on LPS stimulated macrophage. The expression of pro-inflammatory cytokine (TNF-alpha & IL-6) as well as pro-inflammatory mediators (iNOS & COX-2) also decreased dose dependently in the treatment with chrysin on LPS stimulated macrophages. Moreover, the chrysin treatment greatly reduced the NF kappa B activation on LPS stimulated macrophages, which was subsequently evidenced by the decrease of NF-kappa B nuclear translocation. Collectively, the present findings stated that, a natural flavonoid chrysin has ability to increase the innate immune response by enhancing the functions of macrophages through inhibition of NF-kappa B activation and explored the strong imunomodulatory potential.