In patients with renal artery stenosis (RAS), the inhibition of renin-angiotensin-aldosterone system can cause deterioration of renal function. Here we present a 75-year-old man who developed acute renal failure after olmesartan treatment. Following discontinuation of olmesartan, his renal functions normalized. His renal Doppler ultrasonography and renal angiography showed findings consistent with bilateral RAS. In this case, unlike those previously reported, renal failure developed with olmesartan for the first time and after only a single dose, which is thought to be a new, safe, and tolerable antihypertensive agent. This is a well-defined effect of angiotensin-converting enzyme inhibitors, in patients with RAS. Also with the increasing use of angiotensin II receptor blockers (ARBs), renal failure associated with ARBs in patients with RAS is rising. The use of olmesartan also requires caution and close follow-up of renal functions for patients who have risk factors.