We describe a case of mesangial proliferative glomerulonephritis (MesPGN), the clinical symptoms of which were exacerbated by aldosterone-producing adenoma (APA). A 45-year-old man, who had had a history of hypertension for several years, presented with renal derangement, with serum creatinine at its upper normal limit and with microhematuria and proteinuria. He also presented with hypokalemia, with a plasma aldosterone concentration at its upper normal limit and plasma renin activity at its lower normal limit. After the administration of spironolactone, we resected his left adrenal gland, which had a nodular lesion as well as aldosterone hypersecretion. The treatment normalized his arterial blood pressure and serum potassium concentration. Although his proteinuria disappeared with the reduction in arterial blood pressure, the microhematuria continued. The administration of losartan because of the histological finding of MesPGN reduced the amount of hematuria. A dissociated response of hematuria and proteinuria to antihypertensive treatment indicated that MesPGN was coincidental with APA.