A depolymerizing process of polylactic acid, wherein the polylactic acid is depolymerized in the presence of a hydrolase in an organic solvent or a supercritical fluid, thereby producing a re-polymerizable oligomer. A producing process of polylactic acid, wherein the re-polymerizable oligomer obtained by the above-mentioned depolymerization process is polymerized in the presence of a hydrolase or a polymerization catalyst.