Disclosed is a resin composition containing a biodegradable resin (A), a polyolefin resin (B) and a dispersing agent (C). The resin composition has a sea-island structure wherein the biodegradable resin (A) is dispersed like islands in the polyolefin resin (B) as the sea component, and the biodegradable resin (A) has an average dispersed particle diameter of not less than 1 nm but not more than 1000 nm. This resin composition contains a biodegradable resin such as a polylactic acid which places only a little burden on the environment, and enables to obtain a molded article having moisture-proofing properties and dimensional stability equal to or higher than those of conventional polyolefin molded articles, while maintaining the productivity of the conventional polyolefin molded articles.