The effect of the catalyst concentration (Ca(II)), the method of deposition on the carbon surface and burn-off on the parameters of the micropore and mesopore size distributions have been established. Modification of the carbon by steam and in the presence of impregnated Ca(II) changes both the microporous and mesoporous carbon structure. The micropore adsorption capacity decreased and the mesopore surface area and the average and the variance of the half-width of the micropore slits increased with increasing burn-off for all of the carbons that were studied. The sensitivity of the parameters that were used for characterizing the porous structure of the activated carbon to the changes in the burn-off is determined by the structure of the raw materials. The greatest effect on the porous structure was exhibited by the activated carbons that were prepared from plum stones and charcoal, while the least change was demonstrated by the activated carbons that were prepared from coking and hard coal. The most appropriate method of catalyst deposition on the surface of the activated carbon is calcium ion exchange compared to the impregnation method for deposition.