Selective synthesis of various versatile compounds from biomass is of great importance to displace traditional fossil fuel resources. Here, homogeneous metal nitrate (M(NO 3 ) x )/(2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) and M(NO 3 ) x /TEMPO/NaNO 2 catalyst systems in glacial acetic acid and acetonitrile, respectively, have been found to be highly active and practically sustainable for selective oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-diformylfuran (DFF) using pure O 2 or even O 2 in air as the oxidant. The catalytic methods enable full HMF conversion with a nearly 100% DFF selectivity at 50 °C under atmospheric pressure using a very simple reaction setup and workup. Mechanistic aspects are discussed. The influences of reaction conditions such as different metal catalysts, catalyst loading, solvents, and reaction temperature on the promotion effect were studied. Meanwhile, the catalyst systems had also good performance for aerobic oxidation of other alcohols.