<b><i>Objective:</i></b> The aim of this study was to investigate the effect of oral supplementation with L-arginine on serum biochemical profile, blood pressure, microcirculation, and vasoreactivity/endothelial function in young controls, and elderly women with and without type 2 diabetes mellitus (T2DM). <b><i>Methods:</i></b> Healthy young (<i>n</i> = 25), healthy elderly (<i>n</i> = 25), and elderly women with type 2 diabetes mellitus (T2DME, <i>n</i> = 23, glycated Hb ≥6.4% and mean of 7.7 years for duration of the disease), aged 18–30 and older than 65 years, respectively, were included in the study. All patients underwent biochemical analysis (fasting glycemia and lipidogram), arterial blood pressure, nailfold videocapillaroscopy (capillary diameters, functional capillary density [FCD], peak red blood cell velocity [RBCV_max] after 1 min ischemia, time to reach peak RBCV [TRBCV_max]), and venous occlusion plethysmography (vasoreactivity), before and after 14 days of oral supplementation with L-arginine (5 g/day). <b><i>Results:</i></b> L-Arginine did not change fasting glycemia and lipidogram, but it decreased systolic, diastolic, and mean arterial pressure in elderly women, increased RBCV_max in all groups, and did not decrease TRBCV_max in T2DME. Capillary diameters and FCD remained unchanged in all groups. L-Arginine improved vasoreactivity during reactive hyperemia and after sublingual nitroglycerin (0.4 mg) in all groups. <b><i>Conclusion:</i></b> L-Arginine supplementation (5g/day during 14 days) was able to improve vascular/microvascular health in the elderly women with or without T2DM.