Sb/Sb2O3 composite nanoparticles ranging in average particle sizes from 57 to 665 nm have been prepared by levitation-jet aerosol synthesis through condensation of the antimony vapor in a mixed flow of an inert gas and oxygen. XRD established the presence of rhombohedral Sb and cubic Sb2O3 crystallographic phases in the nanoparticles. At the first time, it was established, that these nanoparticles exhibit a ferromagnetic behavior. The maximum total magnetization observed in the nanoparticles achieved 0.053 emu/g. An excess paramagnetic susceptibility has also been observed. After a long time of room-temperature aging, the susceptibility decreases, accompany by enhancement in the saturation magnetization. It was established, that a difference between the magnetic contributions at low-temperature (liquid nitrogen) and room temperature alters, depending on the average sizes of NPs. Supposedly, the presence of definite localized states in the Sb/Sb2O3 interfaces on the surface of the nanoparticles, and its mutual interactions, are responsible for the observed magnetic phenomena.