Poly(vinylidene fluoride) (PVDF) nanofiber mats prepared by an electrospinning technique were used as an active layer for making mechanical-to-electric energy conversion devices. The effects of PVDF concentration and electrospinning parameters (e.g. applied voltage, spinning distance), as well as nanofiber mat thickness on the fiber diameter, PVDF β crystal phase content, and mechanical-to-electrical energy conversion properties of the electrospun PVDF nanofiber mats were examined. It was interesting to find that finer uniform PVDF fibers showed higher β crystal phase content and hence, the energy harvesting devices had higher electrical outputs, regardless of changing the electrospinning parameters and PVDF concentration. The voltage output always changed in the same trend to the change of current output whatever the change trend was caused by the operating parameters or polymer concentration. Both voltage and current output changes followed a similar trend to the change of the β crystal phase content in the nanofibers. The nanofiber mat thickness influenced the device electrical output, and the maximum output was found on the 70 μm thick nanofiber mat. These results suggest that uniform PVDF nanofibers with smaller diameters and high β crystal phase content facilitate mechanical-to-electric energy conversion. The understanding obtained from this study may benefit the development of novel piezoelectric nanofibrous materials and devices for various energy uses.