[en] We fabricated a ZnO nanosheet-based piezoelectric nanogenerator with different thicknesses and types of dielectric layers. The electrical outputs from the nanogenerators with polydimethylsiloxane (PDMS) and poly(methyl methacrylates)(PMMA) layers were measured under a constant load and frequency. We found that the electrical output decreased with decreasing the thickness of the dielectric layer. The working mechanism can be explained in terms of the capacitance difference between the dielectric layers. The calculated result for the number of accumulated electrons in the dielectric layer was a constant. This indicates that the capacitance of the dielectric layer plays an important role in deciding the output potential. This result implies that a careful design of the dielectric layer is necessary to improve the electrical outputs of piezoelectric nanogenerators.