Acid-base imbalances and electrolyte disorders induced by proton pump inhibitors (PPIs) are extremely rare. However, under certain conditions, PPIs may cause metabolic acidosis or hypokalemia, probably due to an inhibitory action on the proton pump that contributes to H + and K + homeostasis in the kidney. We herein present a case of marked hypokalemia accompanied by distal renal tubular acidosis in which a PPI appeared to contribute to the pathophysiology of metabolic acidosis.