PURPOSE: To obtain a thick oxide superconducting film having high critical current density by applying paste of calcined powder of an oxide superconductor to a substrate, heating the paste at a temp. at which a nonsuperconducting phase is not formed, melting the superconductor in an inert gaseous atmosphere, slowly introducing oxygen and sintering the superconductor.

CONSTITUTION: Powdery starting material for producing an oxide superconductor is prepd. and calcined. Paste of the resulting calcined powder is produced, applied to a substrate and heated at a temp. at which a nonsuperconducting phase is not formed in an oxygen atmosphere. This atmospheric gas is replaced with an inert gas such as Ar and the produced oxide superconductor is melted. Gaseous oxygen is then slowly introduced and the superconductor is sintered to obtain a thick oxide superconducting film. Since the amt. of a nonsuperconducting phase is reduced and sintering can be allowed to proceed sufficiently, resistance is minimized and large electric current can be allowed to flow.