An insight into the mechanism of cancer invasion through the serosa of digestive organs has not been obtained since an adequate experimental model has not been found. In this report, the mouse abdominal wall was considered as intestinal wall and the invasive pattern of cancer cells into the peritoneum was examined morphologically by means of scanning election microscopy (SEM). The effects of BCG and Levamisole (LMS) on the invasion and growth of cancer were also studied. When Ehrlich ascites tumor cells were implanted into the subcutaneous layer of the abdominal wall, the mesothelial cells became round, and the intercellular space expanded 7 days after the implantation. The tumor cells invaded the intercellular space by the 10th day. The mesothelial microvilli became dence and formed a meshwork 7 days after the tumor implantation in combination with an interperitoneal injection of BCG, resulting in firm intercellular binding. The condition was much more obvious on the 10th day. The enhancement of intercellular binding by BCG may play a role in preventing peritoneal invasion. Administering BCG before tumor implantation was better in preventing than administering it after the implantation. The most effective way was to administer BCG before the implantation, followed by two times a week from the 3rd day after the implantation. When LMS was used, the microvilli became quite dence, but not as much as with BCG. With administration of LMS from the 14th day after tumor implantation regression of tumor growth occurred, although the efficacy of LMS was less than that of BCG.