Ferromagnetic nanoparticles which are produced by reducing, in the presence of a polymer, two or more metals having different reduction potentials twice or more, using two or more reducing agents having different reduction potentials, a material coated with a dispersion of ferromagnetic nanoparticles in which the ferromagnetic nanoparticles are dispersed, and a magnetic recording medium which has a magnetic layer consisting of the material. The ferromagnetic nanoparticles having a holding power Hc of 95.5 kA/m or more, the material coated with the dispersion of ferromagnetic nanoparticles having excellent industrial coatability, and the magnetic recording medium using the dispersion are provided.