The use of activated low density microcellular carbon (LDMC) as a catalysis supporter for nanophase Pt or Pd particles has been successfully developed in this study. The good dispersion and interfacial properties of nanophase Pt or Pd particles on activated LDMC are formed by using an impregnation and sintering process. The interfacial structures are examined by TEM, HRTEM and an image analyst system. No preferred orientation of interfacial bonding has been found between nanophase Pt and activated LDMC. The activated LDMC supported Pt or Pd catalysts have the high reactivity which can complete hydrogenation and oxidation of CO gas at low temperatures (<453 K). The catalytic activity of CO hydrogenation is increased as the size of the nanophase Pt and Pd particles decreases.