It is rare that colon carcinoma and mantle cell lymphoma (MCL) occur one after another in intestines. We found two malignancies of sigmoid carcinoma and MCL in a single patient, who had initially been diagnosed with sigmoid carcinoma and treated with radical resection in our hospital. Good postoperative recovery was reported without recurrence signs, which lasted for 7 years and 5 months until polyps of sigmoid colon were found by colonoscopy. Biopsy and immunohistochemistry revealed MCL, but the patient refused treatment. One year later, MCL was diagnosed again in the transverse colon. The patient is currently under observation and has not received treatment for MCL.