The long-term hygrothermal aging will induce the irreversible damages of epoxy-based anisotropic conductive film (ACF) joints. In this study, hygrothermal environment tests were used to accelerate the degradation of ACF joints in Chip-on-Glass (COG) assemblies. The effects of aging on adhesion strengths were measured by shear mode tests and changes of molecular conformation of ACF material were analyzed by Fourier Transform Infrared Spectroscopy (FTIR). Also, the fracture surfaces of ACF joints were investigated by Scanning Electronic Microscope (SEM). The results show that the ACF adhesion strengths decrease with aging; some chemical modifications occur in the aged ACF joints; the fracture failure mechanisms change with the hygrothermal aging.