The effect of surface treatment of the support on the oxidation of carbon monoxide over carbon-supported Wacker-type catalysts was examined. Temperature-programmed desorption (TPD) and FT-IR were used to characterize the surface functional groups of carbon. XRD patterns and XAFS spectra of the catalysts were measured to determine the structure and the chemical environment of palladium and copper. Carboxylic and carbonyl groups were enriched on the carbon support by the pretreatment of the support with HNO3 or the addition of Cu(NO3)(2) as a copper precursor. These surface groups increased the hydrophilicity determined by H2O-TPD, and promoted the formation of active copper phase, Cu2Cl(OH)(3). This appears to be responsible for the observed promotional effect on CO oxidation when CU(NO3)(2) was added as an additional copper precursor.