The progression of intravenous tumor thrombus in colorectal cancer is rare and reports on its resection are limited. This study reports a case of ascending colon cancer with a tumor thrombus in the superior mesenteric vein(SMV). A 44-year-old woman was admitted to our hospital for right, lower abdominal pain. Dynamic CT revealed an enhanced mass in the ascending colon and a tumor thrombus in the SMV. She was diagnosed with ascending colon cancer and an SMV tumor thrombus. An extended right hemicolectomy was performed. The SMV tumor thrombus extended from the gastrocolic trunk (GCT)to the right gastroepiploic vein and the anterior superior pancreaticoduodenal vein. To remove the tumor thrombus, a wedge-shaped incision was made through the SMV. Pathological examination showed a moderately differentiated adenocarcinoma of the ascending colon with extra-regional lymph node metastasis(No. 6)and intrapancreatic venous invasion. The pathological staging was pT4b, pN0, pM1a, pStage Ⅳa(Japanese Classification 9th edition). The patient was discharged on day 13 postoperatively. After discharge, 14 courses of mFOLFOX6 plus bevacizumab chemotherapy were administered. The patient is currently alive with no recurrence 15 months postoperatively.