Abstract: Objective: Study on the effects of impure lactosucrose (ILS) on growth performance and serum biochemical parameters in weaning-rats in a week.Method: 24 weaning rats were randomly assigned to 3 groups as follows: normal control, ILS high dose group and ILS low dose group, the same basal diet for each group, a week for the experiment, checked each target. Result: The body weight, AGD, ADFI, kidney relative indicator and creatine kinase levels in serum administrated with 100mg/kg·BW ILS were significantly reduced compared to rats in normal control group ( p < 0.05) .The ADFI, creatine kinase levels in serum, concentration of the cholesterol and urea nitrogen in serum were significantly reduced ( p < 0.05) , and the thickness of the colonic mucus layer was significantly increased (p < 0.05) in weaning-rats treated with 200mg/kg·BW ILS compared to rats in normal control group.Conclusion: ILS ameliorated lipid metabolism in organism, maintained the integrity of colonic mucous, relieved stress response, and had negative regulation of growth performance in weaning rats in a week.