Abstract: The electrodes of electric double layer capacitors (EDLCs) were assembled with typical commercial activated carbons, as well as various Mndoped activated carbons prepared on lab scale. The electrochemical performances of these electrodes were characterized by cyclic voltammetry and chargedischarge at constant current. Meanwhile, the adsorption isotherms of potassium ion from KOH aqueous solution onto activated carbons were determined. The experimental equilibrium adsorption data were fitted by Temkin equation, and the adsorption capacities of potassium ion onto activated carbons in KOH aqueous solution (w=30%) were determined. Finally, the relationship between adsorption capacities and specific capacitances of activated carbons was investigated. The results show that the specific capacitances of activated carbon electrodes increase with the increase of adsorption capabilities of electrolyte onto activated carbons. Moreover, there exists a definitive linear relationship between electrochemical performances of activated carbon electrodes and electrolyte adsorption capacities of activated carbons with a linear correlation coefficient of 0.970 5.