Abstract: There is provided a method for stably preparing rare earth (RE) 123 type oxide superconductors exhibiting outstanding superconductive properties in the atmosphere. In the method for preparing RE 123-type oxide superconductors by melting, cooling and solidifying a starting composition containing one or more than two kinds of RE such as Y, Sm, Nd, etc., and Ba, Cu and O as constituent elements to crystallize the RE 123-type oxide superconductors, the quantity of replacement between RE and Ba in "RE 123 crystals to be formed" is controlled by changing the initial constitution of the starting composition, for example, by changing the initial constitution to a more Ba-rich side than a composition on a 123-211 (or 422) tie line on a phase diagram to yield RE 123-type oxide superconductors in the atmosphere, which exhibits a critical temperature of 90 K or above and higher critical current density (Jc) in a magnetic field. A trace amount of Pt or CeO.sub.