Surface properties of Avgamasya asphaltite were investigated by the adsorption method using N2 and CO2 gases. In order to see the effect of ash content and pyrolysis temperature on the surface properties of asphaltite, samples were washed with 15% (v/v) HCI to reduce the ash content, and then pyrolyzed in a nitrogen atmosphere between 773 and 1173 K. Surface areas were calculated from N2 adsorption data by the BET and Dubinin-Polanyi (D-P) equations. Specific pore volumes were determined from N2 and CO2 adsorption data by applying the D-P equation. Pore volume distributions and average pore radius were calculated from N2 desorption data by using the modified Kelvin equation. Surface areas obtained by carbon dioxide (3-300 M2/g) were higher than the areas from nitrogen (2-47 M2 /g). Demineralization and pyrolysis changed the surface properties of samples. Surface areas and specific pore volumes have a maximum value around 873-973 K (pyrolysis temperatures). Pore radius increases to 20 angstrom from 10 angstrom after 1073 K because of corruption in the structure of asphaltite. Pore size distribution indicated the presence of mesopores together with micropores.