PURPOSE: To obtain an oxide-based superconducting material with high transition temperature, narrow transition range and high critical current density, by aftertreatment with an oxygen gas plasma of an oxide-based superconducting material prepared by calcining a mixture of compound(s) of specific element(s) and Cu-compound.

CONSTITUTION: The objective high-performance oxide-based superconducting material can be obtained by treatment with an oxygen gas plasma of an oxide- based superconducting material prepared by calcining a mixture of respective compounds of at least one kind of element selected from Mg, Ca, Sr and Ba, at least one kind of element selected from Sc, Y and lanthanoids and Cu.