Monoclonal antibody FU-W-H6 whose immunoglobulin subclass was IgG2a kappa was produced against gallbladder carcinoma cell line FU-GBC-2. In normal tissue, this antibody has a strong reactivity specific to the mucosa of the gallbladder (14/15, 94%), bile duct (5/5, 100%), and pancreatic duct (4/5, 80%) in comparison with the lack of the gastric mucosa, and colorectal mucosa with statistically significant differences (p less than 0.01). In cancerous tissue, gallbladder cancer (11/12, 92%), bile duct cancer (5/5, 100%), and pancreatic cancer (2/2, 100%) reacted gastric cancer (4/12, 33%), and colorectal cancer (1/16, 6%) with statistically significant differences (p less than 0.05). On the other hand, another monoclonal antibody FU-W-E2 whose immunoglobulin was IgM has specificity to the gastrointestinal or gallbladder cancers. Eleven of 13 (85%) gastric cancers, 12 of 16 (75%) colorectal cancers, and 9 of 12 (75%) gallbladder cancers reacted positively with statistically significant differences with each normal epithelia (p less than 0.05). Immunoelectron microscopical study revealed that the antigen recognized by FU-W-H6 was localized by FU-W-H6 or E2 antigens were suggested to be a carbohydrates on the glycoprotein, and were thought to have relation to sialic acid by treatment of acid Sciff and enzymes. Western blot analysis demonstrated that their molecular weights were about 87000, and 92000.