The effect of weathering on the surface chemical composition and wettability of the oil sand solids and bitumen was studied by contact angle measurement, film flotation technique, XPS analysis, and ellipsometry thickness measurement. It was found that mild bitumen oxidation occurred during ore weathering. However, it has negligible effect on the bitumen surface wettability. In contrast, weathering forced more organic matters to adsorb onto the mineral solid surfaces, which made the solids more hydrophobic. A mechanism on how the organic matters adsorb on the solid surface due to weathering was put forward. The loss of the formation water due to weathering resulted in an intimate contact of bitumen with the mineral solids and thus offered the opportunity for the organic matters to adsorb, which was responsible for the enrichment of organic matters on the mineral solid surface. It was further observed that hot water washing partially removed the organic matters from the solids surface and hence decreased the solids hydrophobicity.