The present invention relates to a thermosetting composition which contains a polymer having a half-esterified acid anhydride group, thus having enhanced water and weather resistance. The thermosetting resin composition comprises (I) a compound having an epoxy group and a hydroxy group, and (II) a copolymer prepared from a radically polymerizable monomer having an acid anhydride group and a copolymerizable monomer, of which said acid anhydride group is substantially completely half-esterified.
