This is a very rare case report of multiple small intestine cancer in jejunal loop of Roux-en-Y re-construction, duodenum and jejunum. A 51-year-old man had undergone total gastrectomy by Roux-en-Y re-construction for Stage III B gastric cancer in 1997. In 2008, he underwent partial jejunectomy and partial ilectomy for ileus due to small intestine adenocarcinoma, located at the jejunum 50 cm distal from Roux-en-Y anastomotic region and at the ileum 20 cm proximal from the ileocecal region. PET/CT suspected a recurrence and peritoneal dissemination, so he had undergone S-1/docetaxel treatment since 2009. In 2010, he was diagnosed as obstructive jaundice due to duodenal tumor revealed by CT. Furthermore, enteroscopy revealed duodenal advanced cancer, type 2 advanced cancer and five polyps in jejunal loop, type 2 advanced cancer and type II a early cancer in jejunum. He could not undergo both pancreatoduodenectomy and choledochojejunostomy because of the invasion to hepatoduodenal ligament. He underwent partial jejunectomy for the advanced cancer in jejunal loop 10 cm proximal form Roux-en-Y anastomotic region and in jejunum 50 cm distal from Roux-en-Y anastomotic region for prevention of ileus.