This invention provides a thermally curable resin copolymer (A), composed mainly of an ethylenically unsaturated monomer (a-1), which produces an acid via decomposition at 150° C. or more, an ethylenically unsaturated monomer (a-2) containing an epoxy group copolymerizable with the ethylenically unsaturated monomer (a-1), and an ethylenically unsaturated monomer (a-3) having a reactive silyl group; a thermally curable resin composition including the thermally curable resin copolymer; a cured film formed from the composition; and a liquid crystal display including the cured film. The thermally curable resin composition has extended storage stability and can be formed into the cured film having good adhesion to a substrate.