Zirconium oxide-based electrocatalysts with multi-walled carbon nanotubes as electroconductive support (ZrCxNyOz/MWCNT) were prepared by oxidation of oxy-zirconium phthalocyanine under low oxygen partial pressure and examined as new non-platinum cathodes for polymer electrolyte fuel cells. The effect of reheating treatment of ZrCxNyOz/MWCNT in the temperature range from 900 to 1200 degrees C for 1 h under nitrogen atmosphere on the activity and stability of the oxygen-reduction reaction (ORR) was investigated. The reheating treatment at 1000 degrees C enhanced the ORR activity because of the formation of oxygen vacancies, which might act as active sites for the ORR. The reheating treatment at temperatures above 1100 degrees C, however, led to the formation of carbonitrides which are unstable under cathode conditions, resulting in decrease in the ORR. activity. The reheating treatment significantly increased the durability of ORR at both low (0.6 V vs. reversible hydrogen electrode (RITE)) and high (1.2 V) potential. The reheating treatment at higher temperatures promoted graphitization of the deposited carbon. Because the degradation in the high-potential region mainly originates from corrosion of the carbon materials, graphitization would be effective to improve the durability. (C) The Author(s) 2015. Published by ECS. All rights reserved.