Comparative adsorption and thermogravimetric studies were carried out for unmodified and modified active carbons in order to examine the applicability of high-resolution thermogravimetry to monitor the changes in their surface properties caused by chemical modification. Adsorbates of different polarity such as water, l-butanol, and hydrocarbons were used to probe the surface of active carbons modified by acidic oxidization. It is shown that thermodesorption data measured for these adsorbates by high-resolution thermogravimetry are useful for quantitative estimation of the changes in the hydrophobicity of active carbons caused by their oxidation.