Ovariectomized (OVX) animal is a typical experimental model for investigation of postmenopausal osteoporosis due to estrogen deficiency in women. Recently, both OVX mouse and OVX rat are commonly used for the evaluation of bone tissues in the animal model. OVX mouse is appropriate for the study of pathogenesis of postmenopausal osteoporosis, since various gene knockout mice are available for the experiments. OVX rat model is widely used for the evaluation and development of new drug compounds for postmenopausal osteoporosis treatments. On the other hand, orchidectomized (ORX) animal model is excellent in the study of osteoporosis due to androgen deficiency in men. Both OVX and ORX animal exhibits marked bone loss with increased bone resorption. We focused on the feature and evaluation technique for bone tissues in OVX and ORX animals.