Mantle cell lymphoma (MCL) of the prostate, either primary or secondary, is a rare entity. This case report examines an 83-year-old male who complained of not only nocturia (2-3 times), but also frequency and urgency of urination. The maximal urinary flow rate was 4.1 ml/sec. A transrectal ultrasound-guided prostate biopsy was advised after a hard enlargement of the prostate was detected; however, it was refused. Therefore, a plasma kinetic transurethral resection of the prostate was performed. Postoperative pathological examinations demonstrated MCL of the prostate. Positive immunohistochemistry for CD5 and cyclin D1 was observed. The diagnosis was confirmed by the introduction of a new diagnostic marker, SOX11. The maximal flow rate achieved was 15 ml/sec following surgery. To the best of our knowledge, this is the first study of MCL being diagnosed using SOX11 as a marker in the prostate. This case should alert clinicians and pathologists to pay close attention to the diagnosis of malignant lymphoma of the prostate. This study provides further insights into the diagnosis and therapy of MCL.