Measurement of the bone length is not used routinely in toxicity studies but used to examine growth and bone toxicity. To investigate the utility of measuring the bone length in toxicity studies and to identify the appropriate site, we evaluated femur, tibia, humerus, and sternum, in a 14-day repeated dose oral toxicity study of Dexamethasone (DEX), which is known to cause growth retardation and osteoporosis, in young, periadolescent, and adult rats. To observe the effect of decreased food consumption, we also evaluated the changes in each diet-restricted group in which the food intake restricted to levels corresponding to that consumed by the DEX-treated periadolescent and adult rats. Significant decreases of the bone length at all the measured sites and histopathological findings in growth plates and/or trabecular bone were observed in the DEX-treated young and periadolescent rats. Significant decreases of the femoral length and decreased trabecular bone were observed in the DEX-treated adult rats. No histopathological changes were observed in any of the diet-restricted groups, while decreases of the femoral length, similar to that in the DEX-treated adult rats were observed in the diet-restricted adult rats. The results suggested that measurement of the bone length in femur, tibia, humerus, and sternum was useful in young and periadolescent rats, and measurement of the femoral length was useful in adult rats. Moreover, our results showed that the decreases in the femoral length in the DEX-treated adult rats were not only related to the DEX-treatment, but were also influenced by the decreased food consumption.