Abstract: The present invention provides a thermosetting high solids coating composition comprising (A) a carboxyl-containing compound, (B) a polyepoxide, and (C) a copolymer prepared by polymerizing monomer components comprising (a) 30 to 50% by weight of vinyltrimethoxysilane and/or vinyltriethoxysilane, (b) 5 to 15% by weight of N-methylol(meth)acrylamide alkyl ether, and (c) 35 to 65% by weight of another polymerizable unsaturated monomer, and a method for forming a topcoat using said composition. The composition of the present invention is highly effective in forming a coating film excellent in resistance to both acids and scratch, and is superior in storage stability and recoat adhesion.