this invention provides a method for manufacturing a nanocomposite thermoelectric conversion material in which phonon - scattering particles having a specific shape are dispersed , reducing thermal conductivity and increasing thermoelectric conversion performance . said method for manufacturing a nanocomposite thermoelectric conversion material , in which oxide phonon - scattering particles are dispersed within the matrix of a thermoelectric conversion material , is characterized by including the following stages : a first stage in which , in a solution , the reduction of a salt is used to precipitate out / grow nanoparticles consisting of elements constituting a thermoelectric conversion material , the polymerization of a precursor is used to precipitate out / grow nanoparticles consisting of an oxide constituting phonon - scattering particles , and a mixture of said nanoparticles is collected ; and a second stage in which a hydrothermal treatment is used to alloy said mixture into composite nanoparticles , which are then sintered . this method for manufacturing a nanocomposite thermoelectric conversion material is also characterized in that in the aforementioned first stage , nanoparticles consisting of a first group of elements that constitute the thermoelectric conversion material are precipitated out or grown before nanoparticles consisting of oxides of a second group of elements that constitute the phonon - scattering particles .