Osteoporosis is the most common metabolic bone disease and caused by multiple nutritional, environmental and genetical factors. Bone mineral density (BMD) is rather strongly under genetical control. A number of candidate genes have been studied with respect to the impact on BMD. Also, gene loci of susceptibility genes for osteoporosis have been identified by family-based association and linkage approaches. In particular, LRP5 is an important molecule involved in the determination of BMD, because its abnormality is associated with osteoporosis-pseudoglioma syndrome or autosomal dominant syndrome characterized by high bone density. These findings may contribute to new strategy to teat patients with osteoporosis.