Abstract: Experimental mouse were treated with three living densities,2,6,and 10 individuals per cage (26 cm×15 cm×15 cm).After a week of the treatment,livers of the mouse were collected for determining the content of lipid peroxides,and the activities of the catalase and the superoxide dismutases with thiobarbituric acid reaction,colorimetry and nitrite-form method,respectively.The content of lipid peroxides in 6 ind.-group and 10 ind.-group was significantly higher than that in 2 ind.-group.The activity of the catalase in 10 ind.-group was lower than that in 2 ind.-group,suggesting that crowding results in the decline of the catalase activity,which induces the increase of lipid peroxides,bringing peroxidatic damnification to the body.