PURPOSE: To develop a stable oxide-based superconducting material by mixing the powders of In2O3 or Sb, Pb or Pb3O4, CaCO3 and CuO in a specified ratio, heating the mixture in the air, annealing the mixture, then forming the mixture and reheating the formed product.

CONSTITUTION: The powders of In2O3 or Sb, Pb or Pb3O4, CaCO3 and CuO are mixed as the raw material. The mixture is heated at 840°C for 8 hr and then annealed to 200°C. The mixture is crushed, mixed and formed into a discoid shape, etc. The formed product is heated at 750-850°C in the air or in an oxygen atmosphere, annealed to about 200°C and then quenched to room temp. As a result, an oxide-based superconducting material having the composition shown by the formula AXBYCaZCumOn (A is In or Sb: B is Pb; X, Y, Z, m and n are atomic ratios, 0<X<5, 0<Y<5, 0<Z<5, 0<m<5 and 0<n<15) free of rare- earth elements and with the critical temp. stabilized at ≥77K is developed.