Abstract: 【Objective】To illustrate the effect of lemon enzyme on reducing fat,weight loss and immune function in mice,so as to provide a theoretical basis for the treatment of hypertension,diabetes and cardiovascular diseases caused by obesity by lemon enzyme.【Method】C57BL/6J mice of SPF grade were fed H10301, a 60% high-fat and high sugar diet for 35 days to establish the obesity model. Then,the mice of the fat model group were gavaged with either a low concentration(310.0 mg/kg),medium concentration(620.0 mg/kg) or high concentration(1240.0 mg/kg) of citrin for 42 days. Orlistat(15.6 mg/kg) was used as a positive control. The mice of the control group were fed with normal diet and normal saline of the same volume. The body weight and food intake were recorded during administration. After administration, the Lee's index,organ index and lipid body ratio were calculatedand the blood lipid levels total triglyceride(TG),total cholesterol(TC),high density lipoprotein cholesterol(HDL-C),low density lipoprotein cholesterol(LDL-C) and glucose tolerance of mice in each treatment group were measured. Tissue sections were prepared to observe the changes in liver lipid deposition and pathological structure and the proportion of lymphocyte subsets in the mouse spleen were detected by flow cytometry.【Result】Fat model groups receiving a lemon enzyme treatmenthad significantly lowered body weight, Lee's index and fat body ratio,of which the treatment with the high concentration of lemon enzyme produced the best improvements:relative to the control group,the body weight and Lee's index of mice were notably and significantly lower (P<0.01,the same below) and the fat body ratio was significantly lower(P<0.05,the same below),with no significant effect on mice food intake(P>0.05,the same below). After intragastric administration of lemon enzyme,the liver index of obese mice decreased significantly,but there was no significant difference in the organ indices of spleen,heart orkidney. The levels of serum TC,TG and LDL-C were decreased in varying degrees compared with the control group,while the level of serum HDL-C increased significantly. Lemon enzyme reduced lipid accumulation in the liver of obese mice, with an improved glucose tolerance. In addition,lemon enzyme increased the proportion of CD4⁺ in the spleen of obese mice and reduced the proportion of CD8⁺. After treatment with the high concentration lemon enzyme,the ratio of CD4⁺/CD8⁺ changed from 1.49±0.11 to 3.20±0.42 in the obese model group. CD4⁺Foxp3⁺ decreased significantly after lemon enzyme intervention.【Conclusion】Lemon enzyme can reduce weight induced by a high-fat diet and improve the poor immune state in obese mice. Therefore,lemon enzyme can be used as a weight loss health food in the adjuvant treatment of chronic diseases.