In the Izu Peninsula, Quaternary volcanoes arearranged apparently on two lines of NE direction. The volcanoes of Ida, Daruma, Tanaba, and Irozaki alkali basalts distribute on the west line in the peninsula (Fig.1). Most of the rocks of those volcanoes range in composition from basaltic andesite to andesite. Only a little alkaline basalt is represented in the southern end of the peninsula. Microscopically, the following rock types are distinguished: olivine-bearing two-pyroxene andesite (type Yd) for Darnma Volcano, olivine-augite andesite～basaltic andesite (IVc,IVb→c) for Ida Volcano, olivine-bearing hypersthene andesite (IId→c) for Tanada. Volcano, two-pyroxene andesite (Vc, Vd→c) for Tenshi and Jaishi Volcanoes, and olivine-augite basalt (IVb) of the Irozaki alkali basalts.