In this study the various dyestuffs in industrial wastewaters Basic Blue 41, Acid Violet 17, Reactive Red 23 was investigated adsorption on fly ash whiche is a waste. Dyestuff adsorption on fly ash carried out in batch system has been investigated as a function of medium pH, temperature and the amount of adsorbent. In the other part of the study, fly ash samples treated using H2SO4 and heat have been studied for dye adsorption. After acid and heat treatment, the specific surface area of the fly ash and the dye adsorption capacity increased. The results of adsorption equilibrium obtained by untreated of fly ash were examined for compliance of Langmuir and Freundlich isotherm models. Dye adsorption systems data were fitted better to the Langmuir izoterm. The Gibbs free energy of adsorption ΔG0 , enthalpy ΔH0 and entropy ΔS0 were calculated using the adsorption isotherms obtained at different temperatures. Negative Gibbs free energy shows the dye adsorption onto flyash is spontaneous.