In this study, we investigated the additive treatment effect of TiO2 as alternative support materials to common carbon black for Pt-based electrocatalysts on electrocatalytic activity for oxygen reduction reaction (ORR). The shape of TiO2 was varied by hydrothermal treatment with various additives, such as urea, thiourea, and hydrofluoric acid. From the results of transmission electron microscopy (TEM) images and ultraviolet-visible spectroscopy (UV-vis) spectra, it was identified that the morphology of hydrofluoric acid (HF)-treated TiO2 was changed into a round shape having lower aspect ratio than other samples, and its band gap was decreased. Notably, the electronic state of HF-treated TiO2 support was changed into highly reduced (electron rich) state which led to the increase of ORR activity, compared to other samples treated with different additives or before treatment. The electrocatalytic characteristics changes after treatment with various additives were investigated by using X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), cyclic voltammograms (CV), and rotating disk electrode (ROE) techniques. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.