Pt3Co/C is known as an active catalyst for the oxygen reduction reaction (ORR). The stability of this catalyst under high temperature and potential conditions is a concern for practical application in fuel cell systems. In this study, we have pursued the possibility of improving the performance of Pt3Co/C under such severe conditions by the addition of ruthenium oxide nanosheets. The initial mass activity of RuO2 nanosheets modified Pt3Co/C was higher compared to that of pristine Pt3Co/C. The improved mass activity is attributed to the increase in accessible active sites for ORR for the composite catalyst. The mass activity after accelerated durability test by potential step cycling between 0.6 and 1.2 V vs. RHE at 60 degrees C for RuO2 ns-Pt3Co/C was 243 A (g-Pt)(-1), which is 1.9 times higher than non-modified Pt3Co/C (127 A (g-Pt)(-1)). Transmission electron microscopy analysis and energy dispersive X-ray spectroscopy of the catalyst after durability test showed that the particle growth and dissolution of cobalt was inhibited by the addition of RuO2 nanosheets. (C) The Author(s) 2015. Published by ECS.