PURPOSE: To form an electrically conductive film with high transparency on a heat resistant substrate, by forming a film contg. a transition metallic salt of an org. acid as the principal component on the heat resistant substrate, exposing the film to an atmosphere of an oxidizing gas, and heating it.

CONSTITUTION: Ink consisting essentially of about 5W30% (expressed in terms of metal) transition metallic salt of an org. acid (A) such as tin octylate, indium oxalate or antimony acetate, about 0W20% resin (B) such as polymethyl methacrylate, and about 50W75% solvent (C) such as butanol, acetone or xylene is applied (i) to a heat resistant substrate such as a glass plate to form a film contg. the transition metallic salt as the principal component. The film is exposed (ii) to an atmosphere of a highly oxidizing gaseous substance such as ozone, chlorine oxide, nitrogen oxide or hydrogen peroxide, and the film is heated (iii) to 300W500°C. The exposing stage (ii) and heating stage (iii) may be carried out in the reverse order or at the same time.