The peroxisome proliferator-activated receptor gamma (PPAR γ) agonists have been reported to have antiproliferative and tumor-suppressive effects. We report a case of 55-year-old man with primary aldosteronism (PA) whose hyperaldosteronism was suppressed with the PPAR γ agonist pioglitazone. He had drug-resistant hypertension, hypokalemia, and diabetes mellitus. The diagnosis of PA was confirmed by the oral sodium loading test (20.5 μg/d of urinary aldosterone) and Captopril challenge test (19.5 ng/dL of plasma aldosterone). Computed tomography imaging revealed no apparent adrenal mass. The result of the posture stimulation test was consistent with the diagnosis of idiopathic adrenal hyperplasia. On administration of pioglitazone (30 mg/d) and nifedipine (40 mg/d), hypertension and hypokalemia improved and plasma aldosterone decreased for more than 6 months. The sodium loading test done after 6 months of the administration revealed the near normal results (11.2 ng/dL of plasma aldosterone and 13.1 μg/d of urinary aldosterone). The findings indicated that pioglitazone suppressed PA.