Effect of weathering on oil sand processability was studied using a good processing ore, a laboratory weathered ore and a naturally weathered ore. The laboratory weathered ore was prepared by weathering the good processing ore in an oven under controlled conditions to study the nature of ore weathering. It was found that the bitumen recovery, bitumen flotation rate, and bitumen froth quality were greatly reduced due to ore weathering. It was also observed that the fresh bitumen coating on a silicon surface could recede and liberate from the silicon surface easily even in a warm water of 35 degrees C. However, after weathering of the bitumen coating, its liberation became more difficult and effective liberation of bitumen from the silicon surface could only occur at higher temperature of 65 degrees C. The current study further confirms that weathering enhanced adhesion of bitumen with solids, causing difficulties for bitumen liberation from sand grains and hence poor processability of weathered ores.