A 33-year-old pregnant female with high blood pressure and proteinuria referred to Pusan National University Yangsan Hospital. Although she was evaluated for secondary cause of hypertension 5 years ago, the results showed no abnormality. Despite of intensive medical treatment, her blood pressure was not controlled and proteinuria was worsened, then termination of pregnancy was done at 20 weeks of gestation. After discharge, her blood pressure was well controlled and proteinuria was improved with use of calcium channel blocker and angiotensin receptor blocker (ARB) in outpatient clinic for 6months. The ARB was stopped for her planning of pregnancy and hypokalemia was observed after discontinuation of ARB. Plasma renin activity (55.9 ng/ml; normal, 0.2-2.8 ng/ml/h) and aldosterone (537.2 pg/mL; normal, 40-310 pg/mL) was markedly elevated. Abdomen CT showed enhanced round mass at the right kidney. Right partial nephrectomy was performed on the patient. The histologic findings confirmed a diagnosis of reninoma. The patient’s blood pressure and serum potassium remained normal after surgery. The diagnosis of reninoma might be delayed in patients taking ARB because ARB masked hypokalemia caused by reninoma.