PURPOSE: To obtain a thin oxide superconducting film having about ≥90K onset temp. by coating a substrate with a soln. contg. metallic complex salts of Bi, Ca, Sr and Cu and by heat-treating the coated substrate at a specified temp.

CONSTITUTION: Org. acid salts of Bi, Ca, Sr and Cu such is naphthenates or 2-ethylhexanates or metallic complex salts of Bi, Ca, Sr and Cu as chelate compds. such as acetylacetonato chelates are mixed in a prescribed ratio and dissolved in a solvent such as terpene. A substrate is coated with the resulting soln., optionally calcined at 500-700°C and heat-treated at 750-900°C.