Exergy analysis is important for all energy resource utilization since it is part of energy analysis. In recent years, exergy analysis has been widely used in the design and performance evaluation of thermal systems. In this study, an exergy assessment and modeling of geothermal power plants is presented. A comprehensive case study is conducted in the Kizildere Geothermal Power Plant (KGPP) in Denizli, Turkey. Using the plant data, an evaluation of the KGPP performance, energy and exergy efficiencies, and exergy destructions in each component of the plant as well as in the whole plant are quantified and illustrated using an exergy flow diagram. In addition, a parametric study on the effect of varying reference state properties on the exergy efficiencies of the KGPP is conducted to find the optimum performance and operating conditions.