Objectives:In view of the prevalence of osteoporosis in Japan, which surveys have shown has almost doubled over the last ten years, contributory factors, additional to the mineral status, that affect bone stiffness have been explored in spontaneously obese (Minko) rats.Methods:Bone stiffness and strength as well as content of Mg, Ca, P, Na, K, and trace minerals in femurs were compared in male and female Minko rats, which have abnormal lipid metabolism.Results:Mechanical study of femurs indicated that bone stiffness of male rats was significantly higher than that of female rats, but that Mg, Ca, P, Na, Zn, Sr and Fe concentrations in male rats were significantly lower than that of female rats, while S and K concentrations in male rats were significantly higher than that of female rats.Conclusions:These results suggest that bone strength isn’t determined only by mineral concentrations such as Mg, Ca and P. We reported that the bone strength of “Minko Rats” was significantly higher than bone strength of control rats, but there was no significant difference of Ca and P concentrations between the two groups of rats.