A polylactic acid-based resin composition composed of a high molecular ingredient (A) comprising polylactic acid (a1) and an aliphatic polyester (B), and a film, particularly an inflation film, prepared from the resin composition. The film comprising the polylactic acid-based resin composition of the invention is biodegradable and excellent in flexibility and resistance to blocking of film and bleeding-out of plasticizer, has no anisotropy in tear strength, and can be suitably used for an agricultural multi-film and garbage bag. When the film of the invention is used for food wrapping, the film prevents fungus growth and contamination of color or odor, and thus can be suitably used.