The aim of this study is to investigate degradation behaviors of the adhesion strength of the Cu/resin (bisphenol F-type epoxy resin) interface in soaking under high humidity and high temperature conditions. Thermal humidity tests and highly-accelerated temperature and humidity stress tests (HAST) were conducted and the adhesion strength was investigated by a tensile test. An air-HAST was also conducted for a comparison. The fracture surface was analyzed by Fourier transform infrared spectroscopy (FTIR) to investigate the degradation mechanism of the adhesion strength. As a result, it was found that the adhesion strength decreases according to soaking and its degradation increases with increasing soaking temperature. Also, the degradation in the HAST is larger than that in the air-HAST. Degree of water absorption in the Cu/resin interface (Dw), which was defined by the results of FTIR analysis, tends to rapidly increase in early period of soaking and saturate afterwards. Even after absorbing water in the resin by soaking saturated, water infiltrating in the Cu/resin interface induced the formation of copper oxide and caused a further degradation of the adhesion strength. From the Arrhenius plot of the deterioration life of the adhesion strength which was determined by Dw, different tendencies were found in the regions before and after the glass transition temperature of the resin. Thus it was suggested that the life prediction equation for each region is required.