A gravity survey was carried out to estimate fault structure of the Miyakata fault in Ikoma City, Nara Prefecture. The result shows the basement at the western part of the fault is about 200-300 meter lower than that at the eastern part. And a north-south trending basin structure is recognized along the western side of the Miyakata fault. The geological survey for the Ikoma City region reported that the Plio-Pleistocene sediments in this area were deposited about 1Ma ago. After the deposition of these sediments, the Ikoma mountain ranges upheaved. This fact shows the average rate of vertical displacement of the Miyakata fault is about 0.2-0.3mm/yr.