D2 lymph node dissection in laparoscopic surgery for early colon cancer requires selective vessel dissection, making it technically very difficult. Using surgical simulation-CT colonography (simulation-CTC), we could perform laparoscopic assisted sigmoid colectomy preserving the inferior mesenteric artery (IMA) and vein (IMV) more accurately and safely. The case described here was a type 0-Ip sigmoid colon cancer with a tumor size of 13 mm. Endoscopic mucosal resection was performed to confirm a pathological diagnosis of pT1b (4,000 mm) and v1. Sigmoid colectomy was planned, and simulation-CTC was performed, which demonstrated that the cancer was located in the proximal sigmoid colon and supplied by the first sigmoid colon artery (S1). To maintain the blood flow to the distal sigmoid colon, selective S1 resection preserving the IMA and IMV was planned. At the operation, S1, which branches off from the IMA near the bifurcation of the abdominal aorta, was dissected, and the vein accompanying S1, which branches from the IMV in the same area as S1, was dissected. The operation was performed accurately according to the plan, showing that simulation-CTC can be very useful.