Primary small bowel cancer is relatively rare and presents difficulty in preoperative diagnosis. We experienced a case of primary jejunal cancer which was successfully diagnosed by upper gastrointestinal series preoperatively. A 39-year-old woman was seen at the hospital because of an upper abdominal pain. Upper gastrointestinal series revealed a displacement at the greater curvature of the body of stomach and an apple core sign in the jejunum. The patient was diagnosed as having a primary jejunal cancer. Partial excision of the jejunum was carried out. The patient is doing well as of 3.5 years after the operation. Our experience with this case would emphasize the importance that we should entertain a possible presence of small bowel cancer for exploring some lesion in the upper gastrointestinal organs, leading to early detection and improved longterm outcome of the disease.