A case is described in which both a moderately elevated villous adenoma associated with adenocarcinoma at the posterior wall and an independent gastric carcinoma at the anterior wall were present. These two lesions were surrounded by the mucosa of incomplete intestinal metaplasia. Consecutive sections of the villous adenoma associated focally with carcinoma and the independent cancer were stained by the periodic acid-Schiff (PAS), pH 2.5 alcian blue (A1-B1), high iron diamine pH 2.5 alcian blue (HID-AB) and carcinoembryonic antigen peroxidase-antiperoxidase (CEA-PAP) methods. Villous adenoma was weakly positive in the PAS stain but negative in A1-B1 and HID stains, showing that it did not produce mucin. On the other hand, the intestinal metaplasia and cancerous lesions were positive in PAS, A1-B1 and HID stains, indicating production of the intestinal type of mucin. The villous adenoma accompanied by malignant changes was positive by the CEA-PAP method. This result shows the biological property of villous adenoma that they can easily change into malignancy. These three lesions in our case are considered to have originated independently from the primordial cells and to have developed the differences in mucin production in the process of cell development.