Because of the expected long spin-transport length of organic materials, the magnetic metal/organic interface is crucial to the application of organic spintronics. In this study, [Fe/C60]3 multilayers were fabricated for the investigation of C60-mediated magnetic interlayer coupling. [Fe/C60]3 thin films were characterized using the magneto-optical Kerr effect, transmission electron microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS). The thin films revealed in-plane magnetic anisotropy, and the magnetic coercivity (H c ) drastically decreased from 6-8 mT to 0.5 mT with the increase of C60 thickness from 0.1 nm to 5 nm. The insertion of the C60 layer considerably reduced H c because a thickness greater than 1 nm of the C60 layer is sufficient for blocking magnetic exchange coupling between Fe layers. In addition, post-annealing increased H c because of Fe inter-diffusion, which promotes magnetic exchange coupling and further Fe-C bonding, as confirmed by a comparative study of XPS C-spectra. The thermally triggered inter-diffusion between Fe and C60 layers turned the multilayers into a mixed composite film and thus caused magnetic variation. Annealing time and temperature can be used as control parameters for the tuning of magnetism in Fe-C60 composites.