Adenosquamous carcinoma of stomach is a mixed glandular-epidermoid tumor where both components are neoplastic. Its incidence is extremely rare. The five theories on the origin of squamous components are 1) island of ectopic squamous epithelium in the gastric mucosa, 2) squamous metaplasia of gastric epithelium, 3) squamous differentiation in a preexisting adenocarcinoma, 4) endothelial cell differentiated toward squamous elements, and 5) totipotential undifferentiated cells of the gastric mucosa. We experienced three cases of adenosquamous carcinoma. Case 1 was a 71-year-old female patient. ; an ulcerative lesion was present in the pylorus, measuring 5cm in diameter. Case 2 was a 57-year-old male patient. ; an ulcerative lesion is present in the pylorus, measuring 6 em in diameter. Case 3 was a 58-year-old female patient. ; an ulcerative lesion was present in the body and fundus, measuring 10cm in diameter. Microscopic examination revealed a mixed malignant squamous and adenomatous component.