Methods of manufacturing metal oxide nanoparticles are provided. The method uses a bubble generation ultrasonic synthesis method. A gas is injected into a metal oxide preliminary composition solution to promote length growth of nanoparticles. After a basic chemical species solution is mixed with the metal oxide preliminary composition solution, ultrasonic waves are applied to form a reactant. The reactant is refined to manufacture metal oxide nanoparticles. The nanoparticles may have excellent dispersibility and a uniform thin film may be formed by the nanoparticles.