The present invention provides a process for forming a silica-based coating film, characterized by heating a reaction mixture comprising a silicon compound (A) represented by Si (OR).sub.4 and/or a silicon compound (B) represented by R.sup.1.sub.nSi (OR.sup.2).sub.4-n (wherein n is an integer of from 1 to 3), an alcohol (C) represented by R.sup.3CH.sub.2OH and oxalic acid (D) in specific ratios, at a temperature of from 50 to 180.degree. C. in the absence of water, to form a solution of a polysiloxane having a number average molecular weight, as calculated as polystyrene, of from 2,000 to 15,000, applying a coating fluid containing such a solution on a substrate surface, and thermally curing a coating film obtained by such coating, at a temperature of from 80 to 600.degree. C., and such a coating film having a film thickness of from 0.5 to 5 .mu.m, a coating fluid to be used for such a coating film, and a process for producing such a coating fluid.