Highly controlled steam pretreatment was employed to improve the surface properties of activated carbon (AC) which was extensively applied as electrode materials for electrical double layer capacitor (EDLC). The steam pretreatment at 700 degrees C followed by hydrogen (H-2) gasification was found to be the optimal condition for enhancing the surface area, pore size and pore volume of AC. Structural and surface analysis revealed the significant reduction in hydroxyl groups after H-2 gasification during the steam pretreatment on AC. The electrochemical characterizations aroused the considerable improvement in the electrocatalytic and capacitive properties of AC electrode after the steam pretreatment at 700 degrees C. Fabricated EDLC with bare AC electrode exhibited relatively low capacitance of 155.2 Fig, whereas EDLC with steam treated AC electrode showed the appreciable increment in the capacitance of 187.2 Fig which might be due to improve surface area, and pore volume. The steam-treated AC electrode presented the excellent stability by recording 92% of initial capacity after 1000 cycles. (C) 2017 Elsevier B.V. All rights reserved.