PURPOSE: To obtain an R-T-B rare earth plastic magnet where its resistance to oxidation is improved at a low cost, by treating surfaces of a magnetic powder with an organic metal compound containing in advance alkoxy and amino groups in a molecule.

CONSTITUTION: After mixing and kneading an R2T14B system (where R represents rare earth elements containing yttrium and T is transition elements, and B is boron) magnetic powder with additives which consist a binder having principally organic polymer and lublicant and the like, a plastic magnet is obtained by performing compression and injection moldings of them. Then, surfaces of the magnetic powder are treated by an organic metal compound containing in advance alkoxy and amino groups in a molecule. Thus the R-T-B rare earth plastic magnet where its resistance to oxidation is improved can be obtained at a low cost.