Danthron has been shown to induce apoptotic cell death, and inhibit migration and invasion of human gastric or brain cancer cells in vitro. However, there is no report addressing whether danthron affects murine leukemia cells or immune responses in vivo. Herein, this study focused on the in-vivo effects of danthron on WEHI-3 leukemia in mice and immune responses in vivo. The results indicated that danthron reduced spleen weight and increased the percentage of cells with CD3 and CD19 markers, indicating that differentiation of the precursors of T- and B-cells was promoted in the leukemic mice. The results also showed that danthron promoted the activity of phagocytosis by macrophages isolated from the peritoneal cavity but had no effect on peripheral blood mononuclear cells. Danthron also promoted natural killer cell cytocytic activity at an effector and target cell ratio of 100:1 in comparison with leukemic animals in vivo. Taken together, these results demonstrated that application of danthron might affect WEHI-3 leukemia in mice and modulate immune responses in vivo.