The greatest weakness of polymeric materials such as rubber and plastic is to be easy to deteriorate than inorganic or metal materials. Therefore, degradation troubles and lifetime of rubber and plastic products are strongly dependent on their degradation. In order to develop more reliable products, it is necessary to elucidate degradation phenomenon found in the market products. The qualitative analytical method for identification of degradation factor and quantitative analytical methods for the degree of degradation for the cross-linked rubber are introduced.