Hypoparathyroidism (HP) of infant is very rare but an important disease in childhood. Because the symptom of its onset in this period is mainly generalized convulsion due to hypocalcemia. So immediate discrimination from many other diseases caused generalized convulsion must be needed. In this chapter, its clinical symptoms, diagnosis and treatment are described. With the recent advance of molecular biology, abnormalities of PTH gene in familial idiopathic hypoparathyroidism have been discovered. In near future, the analysis of PTH gene will be more helpful about the diagnosis and the treatment of HP.