Abstract: The present invention relates to a method for preparing metal oxide nanoparticles and metal oxide nanoparticles prepared thereby. The method includes: dipping a cathode and an anode formed of a metal for forming oxide, in an inorganic electrolyte solution containing halogen salt, and applying voltage to the anode and the cathode to form, on the anode, metal oxide forming an anode surface. According to a method of the present invention, disadvantages of typical nanoparticle synthesizing methods may be solved to cheaply and rapidly manufacture nanoparticles having various structures through a single process without using a surfactant. In practicing a method of the invention, metal oxide nanoparticles may be rapidly formed, nanoparticles having excellent crystallinity may be produced, and factors of the anodizing method, such as voltage, temperature, an electrolyte, and an electrolyte concentration may be changed to simply adjust a shape of the nanoparticles.