In this study, activated carbon (HHPAAC) was prepared from hazelnut husks using phosphoric acid activation and characterized by some physicochemical analyses. Surface area and zero point charge of pH (pH_PZC) were found to be 770 m² g⁻¹ and 4.5, respectively. Removal of methylene blue (MB) from aqueous solution was performed using a batch technique for determination of the effects of initial pH, contact time, dosage, and temperature. Adsorption of MB was elevated with increasing pH and temperature. The equilibrium data were analyzed by Langmuir and Freundlich equations, and it was found that the data were reasonably well represented by the former with an adsorption capacity of 204 g kg⁻¹. Change in Gibbs free energy (ΔG), entropy (ΔS), and enthalpy (ΔH), were also calculated. Adsorption kinetics were pseudo-second order.