The purpose of this study is to investigate the effects of moderate static magnetic field (SMF, 0.2-0.4 T) on experimental murine leukemia and its possible mechanism. As in vivo and in vitro models, normal mice, mice bearing L1210 tumor and L1210 cell line were exposed to moderate SMF, respectively. The results showed that the average lifetime of mice bearing L1210 was prolonged to 12 days by SMF, but just 6 days in the unexposure group. After being exposed to SMF for 10 days, the spleen and thymus index of normal mice increased. The L1210 cell proliferation was suppressed by SMF within the first 3 days but enhanced in the following 2 days. These results suggested that the regulating effects of SMF on immune functions may have potential contribution to tumor therapy.