Atherosclerosis is driven both by hyperlipidemia and inflammation. Chitin oligosaccharides (NACOS) have shown pharmacological effects on multiple diseases via hypolipidemic and/or anti-inflammatory activities. The present study aims to evaluate whether NACOS treatment can prevent atherosclerosis induced by a high-fat-diet (HFD) in Apolipoprotein E-knockout (ApoE-/-) mice. Results showed that 300 and 900 mg/kg b.w./day NACOS supplementation for 14 weeks significantly decreased atherosclerotic lesions up to 45% and 67% in compared with the HFD (P < 0.05), as measured in the valve area of the aortic root. Further, NACOS supplementation significantly reduced the serum hyperlipidemia and circulating proinflammatory cytokines including interleukin-1β, interleukin-6, monocyte chemoattractant protein-1 and tumor necrosis factor-α. NACOS decreased the hepatic Hmgcr to reduce cholesterol synthesis, activated the genes involved in reverse cholesterol transport to enhance cholesterol efflux and excretion, and reduced the intestinal Npc1L1 to lower cholesterol absorption. Additionally, NACOS enhanced cecum short chain fatty acids production and intestinal integrity. Thus, NACOS supplementation ameliorated atherosclerosis via altering lipid metabolism and reducing inflammation. These findings indicate that NACOS may be a potential functional food material for attenuating atherosclerosis development.