Osteoporosis is a systemic skeletal disease characterized by bone fragility and susceptibility to fracture risk. Bone fragility and fracture risk primarily reflect the integration of bone density and bone quality. Micro-computed tomography (CT) and clinical CT are useful techniques for assessing osteoporosis and predicting fracture risk. Micro-CT is useful for assessing 3D trabecular bone structure. Quantitative CT (QCT) and peripheral QCT (pQCT) are promising tools for the measurements of the bone density. CT-based finite element method (FEM) may provide some useful information about bone mechanics and predict bone strength and fracture site. The usefulness and the limitations of these techniques are reviewed in this paper.