Effects of swimming on bone density and mechanical properties of femur were investigated in aged male and female mice. R/1 strain of senescence accelerated mouse (SAM) at eleven months old was used. Two groups of males and two groups of females each consisting of 7 mice were used. One male and one female groups were loaded with a swim regiment of 40 min a day, 5 days a week for 6 consecutive weeks. The remaining groups were used as the controls. All mice were fed with the standard diet and water ad libitum during the experiments. The results of this study indicated that (i) the body weight was significantly (P < 0.05) lower in the swimming groups than in the control groups in both sexes. (ii) The bone density was significantly higher (P < 0.05) in the swimming groups than in the control groups in both sexes. However, there was no significant difference in cortical thickness index. (iii) In the mechanical properties of bone, there were no significant differences in the level of the maximum breaking force, the ultimate stress and the deformation between the swimming and the control groups in both sexes. However, the elasticity of the bone of the female mice in the swimming group was significantly higher (P < 0.05) than that of the control group. These results suggest that regimented swimming for the aged mice might suppress age-associated bone loss, and the effect of exercise in the females is greater that in the males.