In this study, aerobic oxidation of S-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) was studied over a magnetic catalyst [Fe3O4@SiO2-NH2-Ru(III)]. Various reaction parameters were optimized for the oxidation of HMF into DFF. A high DFF of 86.4% and HMF conversion of 99.3% were obtained after 4 h at 120 degrees C. More importantly, the catalyst also showed high catalytic activity in air, and high HMF conversion of 99.7% and DFF yield of 86.8% were obtained after 16 h. The high catalytic performance of Fe3O4@SiO2-NH2-Ru(III) in air makes this method much more convenient and economical. Moreover, the procedure of the catalyst recycle was simple as the Fe3O4@SiO2-NH2-Ru(III) catalyst could be readily recovered from the reaction mixture by a permanent magnet. The catalyst could be reused several times without significant loss of its catalytic activity.