Abstract: Geothermal power generation has been generally provided by moderate-high temperatures fluids at deepgeothermal zones in water-dominated reservoirs. For these systems, controlling of thermodynamically changes ofliquid phase and monitoring of temperature and pressure effects on geothermal fluids have great importance toprovide of geothermal system sustainability.In a geothermal system, to provide a good information on reservoir rocks types, water-rock interaction and geothermalfluids compositionwill be important to prevent some problems such as; scaling, corrosion etc. during operationalstage of geothermal power/heat systems.The discovered geothermal systems have water-dominated type in Turkey. Büyük Menderes Graben and GedizGraben are two of the largest graben systems in Turkey and there are more than 30 geothermal power generationsystems on these moderate-high temperatures geothermal fields along these graben systems in Western Anatolia.All these geothermal systems have scaling problems such as calcite and silica and they directly affect performance  of the geothermal energy systems. To prevent these problems geochemical modeling studies and geochemical testshave been performed before operational stage of power generation systems. Sustainability of the system directlydepends on determination of scaling types, selection suitable scale inhibitors and installation of inhibitor systemsfor a geothermal system.In this study, scaling tendency of geothermal fluids depends on reservoir geology and the most effective scaleprevention methods at different type geothermal power plantshave beendiscussed for moderate-high geothermaltemperature reservoirs in Western Anatolia and Kızıldere-II (Denizli) Geothermal Power Plant has selected as acase study to explain importance of suitable methods to prevent scaling.