The oxidations of CO and C3H6 are important model reactions for environmental cleanup reactions such as the purification of automotive exhaust gases from diesel engine or of volatile organic compounds. Mn-modified hexagonal YbFeO3 (Mn-h-YbFeO3), synthesized by a solvothermal method, exhibits excellent catalytic activities for these oxidations despite the absence of platinum-group metal (PGM) loading. The activity of Mn-h-YbFeO3 itself is dramatically enhanced by the addition of a small amount of Pd or Ru; these species supported on the Mn-h-YbFeO3 act as promoters that improve the CO- or C3H6-adsorption/desorption ability and the oxygen release property from the Mn-h-YbFeO3. PGM/Mn-h-YbFeO3 catalysts show much higher catalytic activities than Al2O3-supported PGM catalysts in which Al2O3 support is inert for these reactions. We expect that the establishment of such promoter effects for catalyst support having high catalytic activity will provide novel guidelines for reducing the use of precious-metal resources.