In the recent, increased concern has been focused on the pharmacology and clinical utility of herbal extracts and derivatives as a drug or adjunct to chemotherapy and immunotherapy. Salicis Radicis Cortex, A decoction has been mainly used for improvement of ozena and a diuretic effect in oriental medicine, but there was no study on the molecular mechanism of Salicis Radicis Cortex as an immunomodulator. Here we investigated the role of the aqueous extract of Salicis Radicis Cortex in the expression of inflammatory mediators, surface molecule, and related receptors in vitro and in vivo. In murine macrophage RAW 264.7 cells and peritoneal macrophages of C57BL/6N mice, water extract of Salicis Radicis Cortex increased the production of secretary TNF-alpha and Nitric oxide, and the expression level of CD14, LPS co-receptor and CD86, co-stimulatory molecule compared to negative natural extract ex vivo. Moreover, i.p. injection of water extract of Salicis Radicis Cortex significantly increased the secretion level of IFN-gamma and TNF-alpha, IL-2, IL-4 and IL-5 in serum of mice in vivo. Taken together, these results suggest that Salicis Radicis Cortex may regulate the immune response by secreting Th1 and Th2 types of cytokines in vivo and the possibility of its as natural immunostimulator.