Hypophosphatsia is caused by the defect of tissue-nonspecific alkaline phosphatase (ALP), and exhibits hypomineralization of skeleton and rachitic change of bone. The most severe form of hypophosphatasia is a perinatal form, which is also called a lethal form. However, some patients of this form can survive due to advances in neonatology. Other forms consist of infantile, childhood, adult and odonto types. Conventional therapies for hypophosphatasia are administration of vitamin B6 for convulsion and low calcium-containing milk for hypercalcemia. Bone marrow transplantation has been reported to treat several patients with hypophosphatasia. However, the method must be developed which improves the survival of donor mesenchymal cells in patients. Recombinant bone-targeted ALP therapy is now on clinical trial in Canada and U.S.A and expected to be available in near future.