Objective To evaluate the biomechanical effects of low calcium diet on male and female rat femur and compare the biomechanical difference between male and female rat. Methods Sixty 3 -month - old Sprague - Dawley male and female rats were randomized into three groups: control group , very low calcium diet group (VLCD) and low calcium diet group (LCD) . After 90 days, all rats were killed. The left femur from each rat was obtained for three - point bending test. Results Comparing with control group, VLCD and LCD group had no significant difference in biomechanical properties in female rats. Biomechanical properties in male rats also had no significant differences between LCD and control group, but male rats of VLCD had significantly lower maximum load, energy absorption and stiffness than those of control group. Conclusion The results indicated biomechanical properties in male rats were reduced more than those in female rats with the effect of low calcium diet, which body weight may play an important role.