Tungsten disulfide (WS2), which is one of the most common transition metal dichalcogenides (TMDCs), has received great attention in recent years owing to their outstanding carrier mobility, chemical functionality, and optoelectronic properties. However, only few attempts have been reported to access its electromechanical characteristics. Herein, we investigate the intrinsic piezoelectricity of monolayer WS2 nanosheets (NSs) synthesized by chemical vapor deposition (CVD) and estimate their effective piezoelectric coefficient d33 by piezo-response force microscopy (PFM). Moreover, the as-grown WS2 NS was further fabricated into a piezoelectric nanogenerator (W-PENG) to evaluate their energy harvesting capability within nanoscale dimension. More importantly, the W-PENG was applied as self-powered strain sensors with high sensitivity, and integrated into a smart gesture recognition system. These results demonstrate that the W-PENG has great potential for future strain-modulated electronics, ultrathin functional sensors, and human-machine interface design.