A nanocomposite thermoelectric conversion material (100) includes a crystalline matrix (102) made of a thermoelectric conversion material; and phonon-scattering particles (108) dispersed in the crystalline matrix (102). Each phonon-scattering particle (108) includes at least one amorphous nanoparticle (106) coated with a crystalline film (104) having a nano-order thickness, and the crystalline structure of the crystalline film (104) is different from the crystalline structure of the thermoelectric conversion material. The nanocomposite thermoelectric conversion material (100) is produced by i) precipitating a matrix-precursor oversaturated with one element of the thermoelectric conversion material, around the amorphous nanoparticles, thereby producing nanocomposite particles, and heat-treating the nanocomposite particles, or ii) by precipitating only one element of the thermoelectric conversion material around the amorphous nanoparticles, thereby producing first nanocomposite particles, and then, precipitating the matrix-precursor made of the thermoelectric conversion material, around the first nanocomposite particles, thereby producing second nano composite particles, and heat-treating the second nanocomposite particles.