PURPOSE: To prepare a curable resin compsn. which is useful as various coating resins, adhesives, various binders and the like curable through crosslinking at room temp. or by heating by incorporating a crosslinking agent reactive with a hydroxyl group in a lactone-modified polyvinyl acetal resin.

CONSTITUTION: A curable resin compsn. comprising (A) a lactone-modified polyvinyl acetal resin represented by the formula I [wherein R represents H, CH3, or C3H7; 1 represents 81.6 to 50-mol%; m is 0 to 10mol%; n is 10 to 50mol%; y is a number greater than 0 to 50; and X represents a unit of the formula II (wherein z is 4 to 8; and Ra and Rb represents H or CH3) prepd. by ring opening of a lactone compd. and X represents the average number of moles of addition when 5 to 60 pts.wt. lactone compd. is used based on 40 to 95 pts.wt. polyvinyl acetal resin], (B) a compd. having a hydroxyl group and a reactive group, and (C) an optional other polyol or epoxy resin. The compsn. is useful as various coating resins, adhesives, processing of fiber products, various binders and the like curable through crosslinking at room temp. or by heating.