To provide a moisture-curing graft copolymer useful for automotive components and coating materials and sealing material for e.g. construction or repair and to provide a coating composition containing the same.

This invention provides a graft copolymer prepared by grafting 70-99wt.% polymerizable unsaturated monomer onto 1-30wt.% cellulose acetate butyrate and having an isocyanato component content of 0.5-28.5wt.% based on the total weight of the copolymer, a weight-average molecular weight of 2,000-150,000 and a glass transition temperature of 0-90°C and a coating composition mainly consisting of the graft copolymer.