The CO/H-2 titration method was used to determine the metal surface area on Ru:Mn/Al2O3 supported system. This method was based on the assumption that CO is selectively adsorbed to form a monolayer on metal surface but is not adsorbed on the support surface and that all the adsorbed CO is hydrogenated to form CH4 selectively. The data indicate that Mn covers the surface of Ru and hence the no of active sites responsible for the production of CH4 is blocked by the addition of Mn. A continuous decrease in the dispersion of the active metal is discussed in terms of ensemble affect generated by the presence of Mn on the surface of Ru.