Objective To investigate the regulating effects and mechanism of Laminaria japonica polysaccharide (LJPS) on lipid levels in serum of hyperlipenmia rats. Methods Thirtytwo healthy female Wistar rats were used to establish hyperlipemia models by feeding fatrich forage, and treated with LJPS as a potential drug. The serum levels of triglyceride (TG), total cholesterol (TC), low-density lipoprotein (LDL) and high-density lipoprotein (HDL) were determined by biochemical assay. The nitric oxide (NO) level in serum and hepatic tissue was measured by nitrate reductase assay and the activity of superoxide dismutase (SOD) in serum and hepatic tissue was detected by oxidase assay. The level of ox-LDL in hepatic tissue was determined by enzyme-linked immunosorbent assay. The expressions of SOD and inducible nitric oxide synthase (iNOS) in hepatocytes were detected by immunohistochemical assay. Results The rat serum levels of TG, TC and LDL were significantly higher while HDL was lower in the LJPStreated group than those in the hyperlipidemia model group (EM>P/EM><0.05). Both the levels of ox-LDL and NO in both the rat serum and hepatocytic tissues were significantly lower and the activity of SOD was higher in the LJPS-treated group than those in the hyperlipidemia group (EM>P/EM><0.05). The experimental results showed that the iNOS down-expression and the SOD upexpression were found in the LJPS-treated group than those in the hyperlipidemia group (EM>P/EM><0.05). Conclusion Laminaria japonica polysacharide- mi