A 79-year-old man presented with a chief complaint of difficulty in urination. Digital rectal examination and transrectal ultrasonography showed an enlarged prostate. Holmium laser enucleation of the prostate (HoLEP) was performed. Histological findings revealed diffuse large B-cell lymphoma by immunohistochemical studies. Pelvic Lymph nodes were swollen on fluoro deoxygiucose-positron emission tomography examination. Therefore, the disease was classified into clinical stage II according to Ann Arbor's criteria. The patient achieved complete response after 6 cycles of combination chemotherapy with rituximab, pirarubicin, cyclophosphamide, vincristine, and prednisolone (R-THP-COP). Now, 1 year 8 months after the chemotherapy, he remains free of the disease.