Ceramic oxide membranes are widely being researched for Carbon Capture and Storage/Utilization sector applications. Foreseen applications of these membranes are oxygen generation for oxyfuel combustion in e.g. power plants, glass-,cement- or steel production. Major drawback with Mixed Ionic and Electronic Conducting (MIEC) perovskite structure membranes is their limited long term stability at high temperatures in aggressive atmospheres. Dual phase composite membranes have been reported to excel overcoming this drawback. In addition to performance evaluation, Ce0.8Gd0.2O2-delta - FeCo2O4 (CGO-FCO) membranes were subjected to stabilitytest in flue gas conditions closely mimicking industrial flue gas atmosphere. The dual phase composites are investigated for their phase stability at the operating temperature of 850 degrees C in a gradient of oxygen chemical potential. The composites were also exposed to a series of gas mixtures over a period of time at their operating temperature to test for the chemical stability. CGO-FCO membranes are identified to possess chemical stability in gas mixtures of CO2, SO2 along with oxygen over a period of 200 h at 850 degrees C under oxygen partial pressure gradient.