Although protection of the kidneys by renin-angiotensin system (RAS) inhibitors is well known, differences in renal protection and the characteristics of RAS inhibitors have not been fully investigated. We randomly allocated 80 patients with hypertension complicated by type 2 diabetes and accompanied by microalbuminuria to 4 groups for treatment with the angiotensin receptor blockers (ARBs) telmisartan, losartan, candesartan and valsartan. Strict anti-hypertensive therapy was performed for 12 months (target blood pressure: lower than 130/80 mmHg), and renal function was compared. At study completion, all groups achieved the hypotensive target and no difference was noted in blood pressure levels. However, influences on renal function differed. In the telmisartan group in particular, the serum creatinine level was unchanged while the urinary albumin level and protein excretion were significantly decreased, displaying a strong renoprotective effect. These findings suggest that, although renal protection is a class effect of ARBs, the effect of telmisartan is particularly strong.