The effectiveness of adsorption for dye removal from wastewaters has made it an ideal alternative to other expensive treatment options. The removal of acid red 183 (AR) and acid green 25 (AG) onto shells of bittim (Pistacia khinjuk Stocks) (BTS) from aqueous solutions was investigated using parameters such as contact time, pH, temperature, adsorbent doses, and initial dye concentration. Adsorption isotherms of dyes onto BTS were determined and correlated with common isotherm equations such as the Langmuir and Freundlich models. Adsorption equilibrium was reached within 30 min. It was found that the Langmuir isotherm appears to fit the isotherm data better than the Freundlich isotherm. Parameters of the Langmuir and Freundlich isotherms were determined using adsorption data. The maximum adsorption capacities for AR and AG onto BTS at 308, 313, and 318 K were found to be 33, 28, and 20; 16, 18, and 7 mg/g, respectively. The adsorption kinetics of AR and AG could be described by the pseudo-second-order reaction model. The data obtained from adsorption isotherms at different temperatures were used to calculate several thermo-dynamic quantities such as the Gibbs energy (Delta G(0)), enthalpy (Delta H-0), and entropy (Delta S-0) of adsorption. The adsorption process was found to be spontaneous, endothermic and physical in nature. Locally available adsorbent BTS was found to have a low cost and was promising for the removal of AR and AG from aqueous solutions.