Formaldehyde (HCHO) is a typical air pollutant capable of causing serious health disorders in human beings. This work reports plasma-catalytic oxidation of formaldehyde in gas streams via dielectric barrier discharges over Ag/CeO2 pellets at atmospheric pressure and 70◦C. With a feed gas mixture of 276 ppm HCHO, 21.0% O2, 1.0% H2O in N2, ～99% of formaldehyde can be effectively destructed with an 86% oxidative conversion into CO2 at GHSV of 16500 h−1 and input discharge energy density of 108 J l−1. At the same experimental conditions, the conversion percentages of HCHO to CO2 from pure plasma-induced oxidation (discharges over fused silica pellets) and from pure catalytic oxidation over Ag/CeO2 (without discharges) are 6% and 33% only. The above results and the CO plasma-catalytic oxidation experiments imply that the plasma-generated short-lived gas phase radicals, such as O and HO2, play important roles in the catalytic redox circles of Ag/CeO2 to oxidize HCHO and CO to CO2.