Aging is associated with endothelial dysfunction, mediated in part by increased oxidative stress. Polyamines (PA) are natural biomolecules with antioxidant effects that also activate autophagy, a cellular damage repair process important for oxidative stress defense. To determine if PA therapy improves endothelial function with aging, we studied endothelium‐dependent dilation (EDD) to acetylcholine in carotid arteries of young (Y: 6 mo, n=7), old (O: 28–29 mo, n=7) and old PA‐treated (OPA: 29 mo, n=7; 4 weeks 3 mM spermidine drinking water) male C57/BL6 mice. Max EDD was reduced with age (O: 79 ± 5% vs. Y: 95 ± 2%, p<0.05), but PA treatment restored EDD to levels similar to Y (OPA: 99 ± 1%, p<0.05 vs. O). EDD was similar among groups in the presence of the superoxide dismutase mimetic TEMPOL, suggesting that the observed differences were superoxide‐mediated. Accordingly, aging was accompanied by increased aortic superoxide production (EPR, O: 4886 ± 630 vs. Y: 2701 ± 516 AU, p<0.05) and greater expression (western blot) of oxidative stress marker nitrotyrosine (NT, + 1.96‐fold vs. Y, p<0.05) and pro‐oxidant enzyme NADPH oxidase (+1.55‐fold vs. Y, p<0.05). PA treatment normalized superoxide production (OPA: 3296 ± 582 AU, p<0.05 vs. O) and reduced NT and NADPH oxidase expression (both p<0.05, OPA vs. O). Further, PA treatment increased expression of the antioxidant enzyme EC‐SOD (OPA: +3.52‐fold vs. Y, p<0.05) and autophagy markers LC3‐II and LAMP‐2a (both p<0.05, OPA vs. O). PA may be a novel treatment for age‐related endothelial dysfunction by reducing superoxide‐associated oxidative stress and stimulating antioxidant defenses, including autophagy. NIH AG013038, AG039210