The present invention relates to a preparation method comprising the steps of: producing nanoparticles in an aqueous phase using electrostatic bonding between an anionic drug and a cationic compound, and incorporating the nanoparticles into a polymeric micelle consisting of an amphiphilic polymer and any polylactic acid salt, to thereby increase the yield for preparing a composition for delivering an anionic drug by raising the anionic drug inclusion rate of the formulation though the increase of electrostatic bonding and hydrophobic bonding.
