The present disclosure relates to a method for producing metal oxide nanoparticles includes a first step of preparing a reaction solution containing a metal complex, an alcohol, and water; a second step of heating the reaction solution for phase-separation under a hermetically sealed atmosphere where the volumetric expansion ratio of the reaction solution reaches 5 to 15%; a third step of holding the reaction solution heated in the second step for 30 minutes or more for dehydrating the metal complex to precipitate the metal oxide nanoparticles; and a fourth step of collecting the metal oxide nanoparticles after the metal oxide nanoparticles are cooled.