Carbon materials especially, activated carbons emerge as an important industrial materials for various applications like energy storage, electronics, photovoltaic etc. owing to their high specific surface area, good porosity and electrocatalytic nature. Activated carbon (AC) materials are commonly used as the electro-active materials in electrochemical double layer capacitor (EDLC) because it is less expensive and excellent chemical/mechanical stability. In this paper, highly controlled steam pretreatment was employed to improve the surface properties of activated carbon (AC) and extensively applied as electrode materials for supercapacitor. The steam pretreatment at 700^oC followed by H₂ gasification was found to be optimal temperature for achieving the high surface area, pore size and pore volume of AC. FTIR and XPS analysis revealed the significant reduction in hydroxyl groups after H₂ 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^oC. The supercapacitor based on bare AC electrode exhibited low capacitance of 155.2 F/g whereas supercapacitor based steam-AC/700^oC electrode showed the appreciably increment in the capacitance of 187.2 F/g which might be due to improve surface area, and pore volume. The steam-AC/700^oC electrode presented the excellent stability by recording 92% of initial capacity after 1000 cycles.