Flammulina velutipes is an edible mushroom and contains a lot of fiber, vitamin $B_1$, $B_2$, niacin and folic acid. This study was conducted to explore the effects of the Flammulina velutipes mushroom on immune cells and immunity. Th1 cytokine productions as $IFN-{\gamma}$, $TNF-{\alpha}$, and IL-2 were measured in an activated macrophage by Flammulina velutipes water extract in seven concentrations (0, 5, 10, 50, 100, 250, 500, and $1,000{\mu}g/mL$). Also, the splenocyte proliferation index was measured at 48 hours after treatment of the Flammulina velutipes water extract in seven concentrations or mitogen, LPS and ConA. The $IFN-{\gamma}$ and $TNF-{\alpha}$ productions were increased by treatment of the Flammulina velutipes water extract. The $TNF-{\alpha}$ production was significantly higher in the $50{\sim}1,000{\mu}g/mL$ Flammulina velutipes water extract treated macrophages. The $IFN-{\gamma}$ production of macrophages treated with the Flammulina velutipes water extract increased significantly in all groups, and the highest $1000{\mu}g/mL$ concentration. The splenocyte proliferation index was enhanced when the $10{\sim}1,000{\mu}g/mL$ Flammulina velutipes water extracts were treated compared to the control. These primary results suggest that Flammulina velutipes may enhance the immune function by activation of the macrophage and spleen cell.