A coating agent composition, comprising (A) 100 parts by weight of a polymer having at least two alkoxysilyl groups, wherein the polymer has a number average molecular weight of 500 to 500,000, the polymer has a principal chain comprising a polycarbonate or a polyarylate, and the alkoxysilyl groups in the polymer have the formula —SiR3−a(OR′)a, wherein R is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms, R′ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 8 carbon atoms, and a is from 1 to 3; (B) 50 to 2,000 parts by weight of an organic solvent; (C) 1 to 90 parts by weight of an organosilane, wherein the organosilane is a compound having the formula R″eSiY4−e or a partially hydrolyzed condensate thereof, wherein R″ is a substituted or unsubstituted monovalent hydrocarbon group or a hydrogen atom, Y is a hydrolyzable group, and e is from 0 to 2; and (D) a cure catalyst in an amount sufficient to cure the composition. A method of preparing a coating agent composition and a coating agent prepared by curing the composition.