An oxide superconductor is capable of assuring a high trapped magnetic field and maintaining its performance for a long period of time without being affected by internal or external forces, such as thermal strain or by corrosive environments. The oxide superconductor contains a resin impregnated layer incorporated with a filler material having a low value of linear thermal expansion coefficient, or contains the resin impregnated layer or a resin impregnated layer incorporated with a filler material and covered with a resin layer incorporated with the filler material having a low value of linear thermal expansion coefficient, or contains an oxide superconductive bulk body having an adhesively covering layer of resin impregnated fabric on the outside surface, or contains an oxide superconductive bulk body having on the surface thereof a resin or a resin-impregnated layer dispersedly incorporated with a filler material.