The thermal degradation of four different types of colorxerographic images was tested under the conditions of 60-80°C in 50-70% RH for 30 days. The degradation was evaluated according to the color difference (Δ E *) in CIELAB, and the content of the degradation was showed as numerical value by analysis of Δ E *. Colorpatches (Y, M, C, W, Black & Neutral Gray) prepared from the full size copy of the Macbeth Color Checker were used as test pieces. The degradation of the images remarkably depended on the grade of copy, kinds of toner and also tested conditions. As the effect of temperature and humidity on the degradation, the former showed higher effect than that of humidity. It was cleared that all tested images showed only the increase of discoloration and no fading from the result of minus values of lightness difference (Δ L *) and saturation difference (Δ C *). It was also cleared that the surface state of copies remarkably changed by thermal degradation test. It was showed from the decrease of surface glossiness value and observed from the reflection microphotograph. This phenomenon is considered to be disorder of multiple toner layers and the permeation of toner layer into base paper. It was considered from these experimental results, that the presumption of life time of the copies by Arrhenius plotting is difficult.