A method for making iridium oxide nanoparticles includes dissolving an iridium salt to obtain a salt-containing solution, mixing a complexing agent with the salt-containing solution to obtain a blend solution, and adding an oxidating agent to the blend solution to obtain a product mixture. A molar ratio of a complexing compound of the complexing agent to the iridium salt is controlled in a predetermined range so as to permit the product mixture to include iridium oxide nanoparticles.