In the present study, metal nanocrystals were obtained by the very easy, economical, and nontoxic thermal decomposition method and stabilized by coating oleate without any solvent. These nanocrystals have a highly crystalline structure due to a high decomposition temperature (∼563−573 K) at low pressure and very narrow distribution. The prepared Fe₃O₄ nanocrystals were controlled by the annealing time and vacuum pressure. A TEM image of monodispersed Fe₃O₄ nanocrystals showed the 2D assembly of nanocrystals, demonstrating their uniformity. The particle size is 10.6 ± 1.2 nm. TEM images of silver nanocrystals a showed 2D assembly with 9.5 ± 0.7 nm. An electron diffraction image and X-ray diffraction of the nanocrystals showed the highly crystalline nature of metal nanocrystals.