To provide a substrate for an oxide superconducting conductor, capable of being made it thinner and of being superior in heat resistance and an oxide superconducting conductor of thinner type having high critical current density.

The oxide superconducting conductor is composed of constituents, which include a metal core substrate 11 of 7-30 μm thickness, a composite material 10 which is prepared with the surfactant materials 12, 13 composed of nickel alloy coated on both sides of the metal core substrate, an intermediating layer composed of a polycrystalline thin membrane, formed on this composite material and the layer composed of the oxide superconducting conductor formed on this intermediating layer.