CFRP is commonly used as external reinforcement on bridges in service; it increases the life of bridges by solving problems such as structural degradation caused by environmental damage. However, CFRP's bond with concrete has some limitations, including durability issues of the bond between CFRP and concrete that are caused by aggressive environmental exposure and fatigue loading. This paper studied the bond behavior of composite sheets bonded to concrete blocks through single-lap shear tests. Three externally CFRP bonded to concrete blocks were tested via fatigue loading under constant range stress. Load-slip curves and the strain profiles in the interface zone are presented as a function of the number of cycles. Moreover, comparison and analysis of failure modes are presented between specimens subjected to static and fatigue loading. In addition, the interface stiffness degradation as a function of the number of fatigue loading cycles is presented in this paper and a damage model was proposed to describe the fatigue damage of the CFRP-concrete interface. The results of this study demonstrate the effect of the fatigue loading on the CFRP to concrete bond behavior, in terms of bond stiffness degradation and mode of failure.