Grand canonical ensemble Monte Carlo calculations were held for Ar-Kr binary solution in slit graphite pores of different width at 88 K. The main aim of the present work was to investigate the dependence of the adsorption properties for binary films on the pore width. It was shown that the graphite pore sizes influence significantly the selective adsorption of krypton only in the range of pore widths less than six molecular diameters. For very thin pores the sizes of MC cells in x and y directions are quite important for adsorption characteristics.