Ungaran geothermal prospect has promising potential of geothermal energy which is located in the Central Java province,Indonesia.Gedongsongo area is the main geothermal field which indicates fumaroles, hot springs, hot acid pools and acid surface hydrothermal alteration zones. A model of underground geothermal fluid flows was presented based on the several geophysical surveys; gravity, spontaneous-potential, micro-seismic, infrared imagery, and shallow depth temperature. The highest gravity anomaly located in the northern part of the summit area of Ungaran volcano and correlates with Old Ungaran volcano. The deep geothermal fluids supplied from below in the central part of the volcano has an enthalpy of 1085 kJ/kg (250oC) and a mass flow of 230 kg/s to 250 kg/s. Up flow of hot water occurs beneath the collapse wall area, and flows laterally, then some portion of the water is discharged at Gedongsongo area. The estimated geothermal potentials is 40.4 MW with assume as 3 km the thicknesses of reservoir.