the present invention relates to a method for preparing metal oxide nanoparticles and metal oxide nanoparticles prepared thereby , and more particularly , to an method for preparing metal oxide nanoparticles , the method including : 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 for preparing metal oxide nanoparticles of the present invention , disadvantages of typical nanoparticle synthesizing methods may be solved to cheaply and rapidly manufacture nanoparticles having various structures through a simple and single process without using a surfactant . since an anodizing method requires only a power supply device having a low voltage of 30 v or less and an electrolyte , and is performed at room temperature , the anodizing method does not require an additional device or installation . also , from just after the power supply device is turned on , 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 . therefore , the present technology is expected to improve economical efficiency of the metal oxide nanoparticles to also contribute to the mass production of the metal oxide nanoparticles .