Abstract: Objective To observe the effect of soybean protein on serum lipids in rats with normal and high-fat diet.Methods Forty eight SPF class Sprague-Dawley rats were randomly divided into 4 groups according to their body weight (soy prote in,casein,soy prote in-high fat,case in-high fat group).The rats were fed with expermiental feedings for 28 days. Then the rats were sacrificed.The serum lipid profile and the level of gene expression were determ ined.Results The con centration of serum total cholesterol(TC)in the soy prote in group was lower than that of the casein group(1.36·0.38 vs 1.97·0.42mmol/L,P < 0.05).The concentration of serum high-density lipoprote in-chloesterol(HDL-C)was significantly higher in the case in group than that of in the soy prote in group(P < 0.05).The concentrations of serum TC,trigly ceride,and low-density lipoprotein-chloesterol in the soy protein-highfat group(1.43·0.22,0.53·0.14,and 0.25·0.06 mmol/L, respectively) were lower than those of in the casein-high fat group(2.03·0.31,0.79·0.20,and 0.31·0.06 mmol/L,re spectively,P < 0.05 for all).The levels of 3-hydroxy-3-methylg lutaryl coenzyme A(HMG-CoA)reductase mRNA and low den sity lipoprotein receptor(LDL-R)mRNA in the rats of soy protein group were significantly higher than those of the rats in casein group.Conclusion Dietary soy protein in take may modulate serumlipid levels through influence the expression of HMG-CoA reduc tase mRNA and LDL-R mRNA.