It is an object of the present invention is to provide a polylactic acid resin composition in which a crystal nucleator appropriate for accelerating crystallization of polylactic acid rein is added.A polylactic acid resin composition comprising a polylactic acid resin, and a metal salt of a phosphorus compound of formula (I) ##STR00001## wherein R.sub.1 and R.sub.2 may be the same or different and are hydrogen atom, C.sub.1-10alkyl or C.sub.2-10alkoxycarbonyl, or a polylactic acid resin composition comprising a polylactic acid resin, and a metal salt of a phosphorus compound of formula (II) ##STR00002## wherein R.sub.3, R.sub.4, R.sub.5 and R.sub.6 may be the same or different and are hydrogen atom, C.sub.1-10alkyl or C.sub.2-10alkoxycarbonyl. The composition is excellent in heat resistance and forming processability.