Small cell carcinoma of rectum is a rare tumor, since the majority of small cell carcinomas are of primary pulmonary origin. This tumor manifested highly aggressive behavior. We reported a 63 year-old male patient who had bloody stool. Colonoscopy revealed a rectal mass with ulcerated surface. Endoscopic ultrasound miniprobe image showed a homogenous, hypoechoic rectal tumor invading into the muscularis propria layer. The diagnosis of small cell carcinoma was made after colonoscopic biopsy, and patient received surgical resection of tumor, followed by chemotherapy and radiotherapy.