Sapphire (alpha-Al2O3) is an important ceramic material that is widely used in substrate material for electronics. We investigate the chemical reaction layer on a sapphire wafer using X-ray photoelectron microscopy (XPS) and atomic force microscopy (AFM). The frictional characteristics of sapphire chemical mechanical polishing (CMP) was studied using in-situ friction force monitoring system. From XPS analysis and AFM experiment, a chemically-reacted layer was verified on the sapphire surface through a chemical reaction between the sapphire and chemicals in a slurry. During sapphire CMP, the friction force mainly depended on the applied pressure. The material removal efficiency per unit friction energy in sapphire CMP was 6.18 nm/kJ.