The ageing of O-2, reduction cobalt-based electrocatalysts prepared by heat treatment (HT) at various temperatures, have been investigated by polarization of the rotating disk electrode (RDE) over a 300-h period in O-2 saturated H2SO4 0.5 N solution. An improved stability of the catalytic performances is realized with the 800 degrees C heat treated samples (HT800). However XPS analysis of the later reveals that no cobalt species are detected on the carbon surface after 100 h of continuous polarization. On the other hand, with the 600 degrees C heat treated catalysts (HT600) a steady decrease of the electrocatalytic parameters (activity, selectivity, ...) is noticed. Hypotheses are discussed concerning the reasons of the deactivation or the stability of the catalysts. Alternative explanations to the participation of cobalt species are especially presented. Effects of the macrocycle loading on the O-2 reduction electrochemical parameters are also considered. Indeed, as expected an optimum value is reached and is close to 3.5 wt% cobalt content.