flax is a food and fiber crop that is grown in some regions of the world . its value will account for its great popularity as a food , medical and cosmetic applications . flax fibers are taken from the stem of the plant and are two to three times as strong as cotton . in this study , we compared brain weight and plasma sex hormone levels in young and aged mice after the administration of linum usitatissimum ( flax seed ) hydro alcoholic extract . in this study , 32 aged and 32 young mice were divided into 4 groups . controls remained untreated and experimental groups were fed with flax seed hydroalcoholic extract by oral gavages during 3 weeks . after 3 weeks , the brain was removed and blood samples were collected to measure sex hormone levels by elisa . data analysis was done by statistical anova test using spss version 18 ( p<0.05 ) . the results of this study shows that the brain weight of mice did not change significantly , but the sex hormone levels in the experimental groups in comparison with the control groups increased significantly ( p<0.05 ) . the hydroalcoholic extract of flax seed had no effect on the brain weight , but this extract improved the sexual hormone levels .