The different grinding characteristics of different crystal faces of a sapphire were compared. A precision grinding test of A-plane, C-plane, M-plane and R-plane for the sapphire was carried out from the grinding force, grinding force ratio, specific grinding energy and surface topography to research their grinding characteristics. Four crystal faces of the sapphire were grinded by a diamond grinding wheel on a precision surface grinder. The grinding forces were measured by a dynamometer, and the grinding force ratio and the specific grinding energy were calculated according to the measured grinding forces. The surface morphology of a workpiece was observed by a scanning electron microscopy. The results indicate that the different faces of the sapphire have different grinding forces, and the C-plane shows the maximum value, followed by the M-plane, A-plane, and the R-plane. The size orders of specific grinding energy are the same as the grinding force. However, the maximum value of grinding force ratio is for the M-plane, followed that by the A-plane and C-plane, and the R-plane is the minimum one. Under the same grinding conditions, the different crystal faces have different grinding material removal modes. The A-plane, M-plane and R-plane are mainly based on brittle fracture, fragmentation and dissociation removal, the crushing pit is larger, and the surface is rough. The C-plane is mainly based on part of the brittle fracture and part of powder removal, the broken crater is smaller, and the surface is relatively smooth. As a results, since the A-plane, C-plane, M-plane and R-plane of the sapphire have different grinding characteristics, they show different grinding mechanisms, grinding forces, grinding force ratios, specific grinding energies and material removal modes.