The effects of diesel oil pretreated with magnetic field on low rank coal flotation were investigated in this study. Flotation results demonstrated that combustible matter recovery increased with the magnetized time (MT) and magnetic field intensity (MFI), then plateaued while concentrate ash barely changed. The highest combustible matter recovery (73.86%) was obtained under 10 min of MT and 0.2 T of MFI. These results coincided with the analyses of interfacial tension and viscosity and supported by the results of SEM and contact angle measurements, indicating that magnetized diesel oil has a beneficial effect on low rank coal flotation.