Low-grade B cell lymphomas of mucosa-associated lymphoid tissue (MALT lymphomas) are mostly seen in the gastrointestinal tract. MALT lymphomas involving kidney are extremely rare. We report on a case of MALT lymphomas of the kidney. A 74-yearold woman presented with an episode of gross hematuria and right flank pain. In renal sonography, we found a hypoecho lesion measuring 61 × 58 × 44 mm in the lower pole of right kidney. A computed tomography scan revealed an enlarged hypodense soft tissue measuring 62 × 42 × 37 mm within the pelvic brim of the right kidney, with extension to the proximal portion of the ipsilateral ureter and engulfed it. The patient underwent a right radical nephrectomy. The pathology specimen indicated a lymphoprolifrative disorder involving the kidney and ureter. To obtain a definitive diagnosis, we used an immunohistochemistry, which confirmed the diagnosis of a MALT lymphoma.