A new Early Triassic ichthyosaurus, Utatsusaurus hataii gen. et sp. nov., is described. The materials were collected from the upper part of the Osawa Formation on the coast at Tatezaki, the Kitakami Massif, Northeast Japan which is correlative of the Prohungaritan-Columbitan ammonoid stages of Spath (1930, 1934). The present form is of the most primitive type of Ichthyosauria from the view point of specialization of the pectoral limb.