By means of the erythrocyte C3b receptor rosett test and the tumor erythrocyte rosette test, we measured the effects of Sepia on the activity of the erythrocyte C3b receptor and the erythrocyte's immune adhesion to tumor cells in normal persons and in malignant tumor patients. The results showed that Sepia has a markedly active effect on the erythrocyte C3b receptor in normal persons and patients with malignant tumor, and this effect was highest when the concentration of Sepia was 10%. Sepia could markedly enhance the erythrocyte's immune adhesion to tumor cells in normal subjects and in patients with malignant tumor, which was more obvious when the concentration of Sepia was 10%. These results indicate that the anti-tumor action of Sepia is related to activating the erythrocyte immune adhesion function.