Co-oxidation of CO and H 2 or oxidation of H 2 in the presence of CO was first achieved at low temperatures (0–20°C) over single-component catalysts (Pd/FeO x ) at a space velocity of 15,000mlgcat-1h-1. A systematical study of FeO x - and Al 2 O 3 -supported Pd catalysts is carried out by means of STEM, TEM, XRD, XPS, Mössbauer spectra, and time-resolved CO titration. Highly dispersed Pd nanoparticles with size 1–1.8nm over 5.4wt% Pd/FeO x are confirmed by HAADF-STEM and HRTEM. Time-resolved CO titration, Mössbauer spectra, and XRD and XPS results suggest FeO x support supplying active oxygen is involved in the oxidations. Particle size effect and oxygen supply from FeO x support are speculated to be the main reasons for the excellent performance of Pd/FeO x in co-oxidation of CO and H 2 or oxidation of H 2 in the presence of CO.