The aim of this study was to investigate whether decreased vasodilation in common carotid artery and abdominal aorta induced by hindlimb unloading (HU) is related with NADPH oxidase pathway.Arterial vasoreactivity was measured by tissue bath, NADPH oxidase expression was observed by western blot, Malondialdehyde (MDA) content was detected by a detecting reagent kit and the oxidation-sensitive dye level DHE was used to detect the level of superoxide anions (O2ˉ).Results showed that (1) Acetylcholine-induced vasodilation was decreased in both vessels by HU, and incubation with Apocynin and SOD could both ameliorate the impaired vasodilation.(2) The level of O2ˉ and the content of MDA both increased significantly in both vessels by HU.(3) The expression of p22phox increased significantly in both vessels and the expression of NOX4 increased significantly in common carotid artery.These results suggest that HU-induced impairment in endothelium-dependent vasodilation is associated with NADPH oxidases alterations.