The objective of this study is to calculate the efficiency of exergy in Germencik Geothermal Power Plant, which has a power output of 47.4 MWe. As being the largest one in Turkey, this plant is operated by double-flash system which is based on the method of analysis of energy and exergy to evaluate its performance. The exergy analysis has been applied to the whole plant considering the first and the second laws of thermodynamics for each equipment. In this study, by using the actual data values the losses of exergy have been determined and the flow diagram of exergy has been illustrated. When making calculations, we have accepted dead state temperature as 15 degrees C, and dead state pressure as 101.325 kPa s. The plant has 7 production and 6 reinjection wells. From these production wells, geothermal fluid reaches the plant at an average temperature ranging from 194 degrees C to 214 degrees C, pressure of 23 bars-30 bars and a total flow rate of 688.87 kg/s. An exergy input of 134,124 kW is obtained from these wells. The largest exergy input of 36,395 kW is obtained from OB-14 and this accounts for 27.1% of total exergy input. Moreover, major exergy losses and their exergy input account for 3.34% (4478 kW) for valves, 22.72% (30,477 kW) for high and low-pressure separation process during the decomposition of geothermal fluid, 5.1% (6837 kW) for turbine-generator during the conversion of steam into mechanic work, 9.41% (12,622 kW) for cooling tower, 5.53% (7414 kW) for internal use, and finally 22.68% (30,415 kW) for reinjection wells. Additionally, the second law efficiency of turbine-generator has been found to be 87.4% and the second law efficiency of overall plant has been found to be 3534%. The obtained results have been given in tables and the largest loss of exergy has been determined to occur in separators. (C) 2013 Elsevier Ltd. All rights reserved.