A method for producing a resin composition, including the steps of melt-kneading a raw material A containing a polylactic acid resin, a crystal nucleating agent, and a plasticizer containing an ester compound formed between a polycarboxylic acid having a hydrocarbon group having 1 to 7 carbon atoms and a mono-alcohol having a hydrocarbon group having 1 to 7 carbon atoms, to prepare a polylactic acid-containing melt-kneaded mixture having a relative crystallinity of 70% or more (step A); and further melt-kneading the polylactic acid-containing melt-kneaded mixture obtained by the step A and a raw material B containing a polypropylene resin and a compatibilizing agent (step B). The resin composition obtainable by the method of the present invention can be suitably used in various industrial applications, such as daily sundries, household electric appliance parts, and automobile parts.