Volcanic products comprise the main visible geological units in the island of Kimolos, southern Aegean Sea (Greece). Very limited outcrops of Neogene and metamorphic formations have been uplifted to the surface by the volcanic domes. Granitic outcrops also reveal the presence of a relatively young nearsurface granite. The interpretation of the Bouguer gravity field proposed in this paper delineates the margins of the concealed mass of the dense metamorphic basement and of the granitic intrusion. The basement appears to be uplifted in almost all the areal extent of the island, plunging to depth outside the island boundaries. Resistivity prospecting, by means of deep electrical soundings, detected the presence of low resistivities in the central part of the island, beneath layers of high resistivities. These results suggest that the granite is heavily fractured, with possibly hot circulating fluids. The resistive cap consists of volcanic material.