Contact angles of apolar and polar liquids were measured on unoxidized and oxidized surfaces of synthetic chalcocite and on chalcocite surfaces covered with potassium ethyl xanthate film formed from aqueous solutions at different concentrations. Then. using the obtained contact angle values, the Lifshitz-van der Waals component and electron-acceptor and electron-donor parameters of the Lewis acid-base component of the surface free energy of chalcocite and chalcocite covered with ethyl xanthate (EX) film were calculated. It was found that the surface free energy of chalcocite originated from apolar and polar intermolecular interaction and that covering the chalcocite surface with ethyl xanthate changed its surface free energy and its components. It was also found that the changes of the surface free energy as a function of the ethyl xanthate concentration from which the films were formed were larger for oxidized than for unoxidized chalcocite. This probably results from the polar character of oxidized chalcocite being higher than that of unoxidized chalcocite and from the difference between the amounts of sulfur present on the unoxidized chalcocite/EX film surface and on the oxidized chalcocite/EX film surface.