A 40-year-old man visited our hospital with rectal submucosal tumors measuring 5 mm and the 7 mm as detected by colonoscopy, following which an endoscopic submucosal resection was performed. Pathological examination revealed that the tumors was neuroendocrine tumor(NET); the tumor measuring 5 mm was NET G1 without lymphatic and venous invasion, while the 7 mm size was NET G2 with venous invasion but without lymphatic invasion. Lymph node and distant metastasis were not observed by computed tomography. Informed consent was obtained and he agreed to undergo additional rectal resection. Laparoscopic low anterior resection was performed and pathological examination enabled a diagnosis of rectal neuroendocrine tumor with regional lymph node metastases(T1a, N1, M0, Stage ⅢB[Union for International Cancer Control 8th edition]). Post-surgery, he was followed up for 3 years, without recurrence. This report suggests that the determination of treatment plan for rectal neuroendocrine tumor measuring less than 1 cm in diameter should be done carefully.