['Orostachys japonicus A. Berger (Crassulaceae) (OJ), well-known as Wa-song in Korea is a medicinal plant with immunoregulatory, anti-febrile, antidote, and anti-cancer activities. This study was aimed at evaluating the immunostimulatory effect of O. japonicus A. Berger and its possible mechanisms of action.', 'To evaluate the effect of OJ aqueous extract on macrophage activity, we evaluated the modulation of macrophage activation state by observing structural (phagocytic activities) and the production of nitric oxide increase. The effect of OJ aqueous extract on RAW264.7 cell viability were assessed using Cell Counting Kit (CCK)-8 assay. HPLC analysis was performed to identify potential active compounds of this extract.', 'The biological investigations indicated that OJ aqueous extract, among others, possessed the highest macrophage activation as indicated by NO production yield. The results showed that OJ aqueous extract exhibited antioxidant effects, which included scavenging activities against DPPH radicals. OJ aqueous extract increased the phagocytic activity of RAW 264.7 cells against IgG-opsonized red blood cells (RBC). The level of phosphorylated Syk kinase was increased in OJ aqueous extract-treated group as compared to control. Phosphorylation of PLC-γ was increased in the OJ aqueous extract-treated groups. Quercetin-3-O-rhamnose and kaempferol-3-O-rhamnose was detected in OJ aqueous extract by HPLC analysis.'] Does aqueous extract of Orostachys japonicus A. Berger exert immunostimulatory activity in RAW 264.7 macrophages?