Lymphoma of the urinary bladder is uncommon, and upper urinary tract obstruction due to lymphoma is rare. Herein, we report a case of malignant lymphoma of the bladder with bilateral hydronephrosis in a 67-year-old female who presented with oliguria. Ultrasonography and computed tomography demonstrated a thickened posterior bladder wall and bilateral hydronephrosis. Whole-body positron emission tomography-computed tomography revealed abnormal accumulation in the right iliac internal lymph nodes. Trans-urethral bladder biopsy led to a histopathological diagnosis of non-Hodgkin diffuse large B-cell malignant lymphoma of the bladder. After bilateral nephrostomy, the patient was treated with six cycles of combination chemotherapy including rituximab, cyclophosphamide, daunorubicin, vincristine, and prednisolone (R-CHOP) and two cycles of rituximab alone. Complete remission was maintained during the 3 years of follow-up.