One-package type composition for in-mold coating is disclosed which contains (a) a urethane compound having at least two acryloyloxy or methacryloyloxy groups at the terminal and at least one 1-oxa-3,5-diazine-2,4,6-trione ring in the molecule, (b) an ester resin having at least one reactive double bond prepared by the reaction of an epoxy compound with an unsaturated carboxylic acid and (c) a vinyl monomer. The composition is useful for coating the molded product from fiberglass reinforced thermosetting polyester resin compounds within a mold. The composition, when coated, shows excellent adherence to the molded product and excellent water resistance.