In a solid oxide fuel cell the cell performance is largely determined by the cathode properties, in particular at low operating temperature (<700{degree sign}C). Intensive cathode studies have made a great improvement in reducing the polarization resistance (Rp) in many systems. This has led to reduction of fuel cell operating temperature to use stainless steel as interconnect, and by this to reduce cost. However, our studies showed a significant increase of Rp over time when samples were kept at low temperature and open circuit voltage. We have systematically investigated these passivation phenomena in LaSrMnO3, LaSrCoFeO3 and BaSrCoFeO3 systems. On the other hand, Rp was reduced significantly by a high temperature annealing, close to the initial value and sometimes series resistance (Rs) could be recovered completely. Cation diffusion and defect disordering are considered to be the main effects contributing to the passivation and activation.