The heat accumulated in the inner parts of the earth's crust is transmitted to the fluid in the geothermal aquifer by means of transportation. The geothermal fluid is transported to the surface either by wells or naturally. In this study, the geothermal fluid in Tuzla geothermal field in Çanakkale city was examined due to its high boron content (10.3 mg L-1). It was aimed to remove boron from geothermal fluid by adsorption in order to prevent possible negative effects on the environment. Fly ash was obtained from Çan thermal power plant. The specific surface area of the fly ash was 14.6 m2 g-1 and the particle size was between 1.45 and 186 µm. According to ASTM C618 standard, fly ash was classified as Class C. Fly ash was composed of anhydrite, lime, hematite, cristobalite, quartz, calcite and feldspar. Various parameters such as initial pH, adsorbent dosage, contact time, and temperature were studied experimentally for the removal of boron from the geothermal fluid. The suitability of pseudo-first-order, pseudo-second-order, and intraparticle kinetic models to experimental data was examined. The data obtained from the isotherm studies were applied to the Langmuir, Freundlich and Dubinin-Radushkevich models.