A resin composition prepared by melting and kneading (A) a thermoplastic resin comprising a polyolefin resin together with (B) a functional compound having one or more bond(s) or one or more functional group(s) selected from the group consisting of non-aromatic carbon-carbon multiple bonds, oxirane groups and substituted carboxyl groups, and subsequently mixing thereinto (C) a polar compound having in one molecule one or more polar group(s) selected from the group consisting of substituted carboxyl groups, substituted hydroxyl groups, substituted amino groups, substituted mercapto groups, substituted sulfonic acid groups, oxazoline groups, isocyanato groups and oxirane groups, provided that at least one of the polar groups of (C) is different from at least one of the functional groups of the functional compound (B), as well as a process for producing said resin composition.