Alginate oligosaccharide (AOS) was reported to possess antioxidant and free radical scavenging activities, but the specific effects and mechanisms remain unclear. We investigated the effects of AOS on H2O2-induced oxidative stress and apoptosis in human umbilical vein endothelial cells (HUVECs) and the associated mechanisms. HUVECs were treated with 100-800 mu M hydrogen peroxide (H2O2) for various periods (12, 24, and 36 h) to establish an in vitro oxidative stress and apoptosis HUVEC model. AOS protects HUVEC cells against oxidative stress-induced apoptosis by decreasing the expression levels of caspase 3 and Bax, and increasing Bcl-2 expression. Microarray assay, real-time PCR and western blot results revealed that AOS was able to effectively suppress H2O2-induced apoptosis via regulated integrin-alpha/FAK/PI3K pathway by influencing the expression of integrin-alpha, FAK, PI3K, PTEN, P21, and CDK2. In conclusion, our study suggests that AOS can protect endothelial cells against oxidative stress injury caused by H2O2, providing novel alternative strategies to prevent atherosclerosis in the future.