Summary.. The anti-tumor effect and mechanism of the staphylococcal enterotoxin A (SEA) werestudied. The mouse gastric tumor model was produced by subcutaneously inoculating gastric tumorcells (MGC80-3). The experimental group was treated with SEA, and the control group was treatedwith normal saline. The percentage of tumor generation and tumor mass was measured. The resultsshowed that the percentage of the tumor generation in the SEA-treated mice was lower than in thecontrol group, but there was no significant difference (P＞0. 05). However, the tumor mass in theexperimental group was significantly lighter than in the control group, with the difference being verysignificant (P＜0. 001). There were more CD+4 T cells and CD+8 T cells in the tumor of the micetreated with SEA than those of the control group. SEA has an obvious anti-tumor effect on mice gas-tric tumor. The mechanism might be that SEA induces the effect of superantigen-dependent cell me-diated cytotoxicity to the tumor cells.