The present invention relates to a polymer nanoparticle freeze-dried product, and a preparation method therefor, the polymer nanoparticle freeze-dried product being obtainable by treating, through a freeze-drying process comprising an annealing step, a polymer nanoparticle aqueous solution comprising an amphiphilic block copolymer, a polylactic acid derivative having a carboxyl terminal group, and a freeze-drying adjuvant, wherein the polymer nanoparticle freeze-dried product is reconstituted within five minutes upon reconstitution by means of an aqueous solvent under atmospheric pressure.
