Proton-conducting perovskite oxides such as doped barium cerate and barium zirconate are promising electrolytes for solid oxide fuel cells (SOFCs). Here we report that the typical high performance proton conductor, BaZr0.1 Ce0.7Y0 2O3 +/-delta (BZCY), is prone to physical, chemical and thereby electrochemical degradations as it ages under ambient conditions. This aging effect destroys the electrolyte disk and breaks down the perovskite lattice. Electrochemical measurements indicate degraded BZCY based SOFC suffers from significant performance losses, and various advanced materials characterization results confirm that this degradation of BZCY is exclusively caused by water and CO2 from the surrounding environment. The water molecules catalyze the degradation, initiating and promoting the carbonatation of BZCY. The subsequent reaction with CO2 creates two major phases: BaCO3 nano-rod single crystals and amorphous oxide mixtures. The entire process is visualized via TEM observations, based on which we propose that this occurs via the microcrucible mechanism. As this mechanism does not incur significant segregations of decomposition products, the aged BZCY powder is easily regenerated by re-calcination. We then study the effects of doping on the stability of BZCY, showing that a higher Zr content obviously improves the aging resistance. (C) 2015 The Electrochemical Society. All rights reserved.