As a possible solution for the cost-effective electrode formation of flexible piezoelectric ZnO nanogenerators, silver-based electrodes are chosen and investigated. The four types of silver-based top-electrodes are fabricated on ZnO thin films by different process conditions or techniques. Results show that the local oxidation of silver-based electrodes in the flexible piezoelectric ZnO nonogenerators can lead to a significant improvement of the device performance in terms of the output voltages. In addition, the ZnO nanogenerators with silver-paste printed top-electrodes, which can be fabricated in a simple and cost-effective way, show a considerably high output performance.