Effects of cyclic deformation and annealing treatment on conductive durability of indium tin oxide (ITO) thin film deposited on polyethylene terephthalate (PET) substrate are investigated. In-situ electrical and mechanical tests of ITO/PET sheet under various combinations of cyclic and static loadings are conducted at room temperature. Experimental results show that the number of cycles to failure is significantly decreased with an increase in displacement amplitude, given a specific extent of electrical resistance change of ITO/PET sheet. A static holding period of 1000. s in various loading modes plays a role in influencing the failure of ITO/PET sheet. Cyclic bending combined with a static tensile holding generally generates more damages and a smaller number of cycles to failure than does that combined with a compressive holding, neutral holding, or no holding. Under a small fatigue loading, the conductive durability of ITO/PET sheet is increased with an increase in annealing temperature. However, there is little effect of annealing temperature on ITO/PET fatigue life under a larger displacement amplitude of fatigue loading. Using a surface-based cohesive modeling technique, a simplified three-dimensional finite element analysis micromodel subjected to tensile and compressive loadings is numerically analyzed to clarify the failure mechanism of interfacial and buckling-like delamination which governs the change in electrical conductivity of ITO/PET sheet. Modeling results indicate that buckle height of the ITO/PET micromodel subjected to tensile loading is significantly greater than that of compressive loading, providing more evidence of the aforementioned effect of loading mode.