Commercial activated carbon (AC) was used as a support either in its original form or after various modifications, giving diverse textural and surface chemical characteristics. The changes of these properties were monitored by N2 adsorption–desorption isotherms, temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Ag catalysts were prepared over the AC supports by a conventional wet impregnation method. The catalytic performances of supported Ag/AC catalysts in the selective oxidation of CO in excess H2 were tested. The results indicate the textural and surface chemical characteristics are responsible for the different catalytic performances.