In this study, methane gas absorption ability of activated carbon (AC) with surface functional group effect, was evaluated after nitric acid and urea treatment of AC surface. Specific surface area and pore distribution of AC were studied through nitrogen absorption isotherm at 77 K. Micro pore volume was calculated through H-K method. Absorbed methane amount was evaluated through volumetric method at room temperature by using auto absorption apparatus. Absorbed methane amount of AC was found to increase with specific surface area increase. Correlation proposed between the methane absorption amount and surface nature indicates that the surface nature plays an important role on the absorption amount at a given temperature.