Rubber o-rings are important sealing components in many vacuum-related processing equipments for semiconductor industry. In those applications, rubber o-rings usually work under a harsh environment subjected to high deformation, high temperature, and chemicals corrosion. In order to perform a successful structural design on o-ring valves, material properties of rubbers are required. In this paper, the elastic properties of a semiconductor grade rubber o-ring, Kalrez AS-568A, are characterized. Due to large deformation and the imcompressibility, the end effect cannot be avoided in uniaxial testing, as a result, digital image correlation techniques is used in conjunction with a self-developed uniaxial testing system to analyzing the deformation. In parallel, an MTS XP nanoindentation system with a Berkovich indentor is also used to characterize the hardness and modulus of rubbers to evaluate the material properties during different periods of service. Soften of rubber is observed with the increase of service period. The initial Young's modulus and the hardness of the rubber are obtained as 9 - 5 MPa and 0.8 -0.5 MPa for different service periods. The test results from both methods are highly correlated and agree to each other. This increases the confidence of the test processes.