NaxCoO2 has a particularly high contact resistance because it forms an insulated layer of NaHCO3 and Na2CO3, which are produced in a chemical reaction with carbon dioxide and water in air on the surface. In this study, we tried to improve the interface resistance between NaxCoO2 and Ag sheet electrodes by connecting these materials with the spark plasma sintering (SPS) technique. The interface resistance between NaxCoO2 and Ag sheet electrodes connected by SPS is compared with that connected with Ag paste. In an experiment, the interface resistance of a sample treated by decrease to less than 1/600 of the former value. It is thought that the NaHCO3 and Na2CO3 insulated layer is decomposed through the application of a large value of applied DC current by using the SPS technique.