Nanofiber-based piezoelectric energy generators could be scalable power sources applicable in various electrical devices and systems by scavenging mechanical energy from the environment. This review article highlights recent advances in nanofiber nanogenerators, discusses their operation principles and addresses performance issues including energy conversion efficiencies and possible false artifacts during experimental characterizations. Piezoelectric nanogenerators made of PVDF (polyvinylidene fluoride) or PZT (lead zirconate titanate) and fabricated by means of electrospinning processes such as conventional, modified or near-field electrospinning (NFES) are the key focuses of this paper. Material and structural analyses on fabricated nanofibers using tools such as XRD (X-ray diffraction), FTIR (Fourier transform infrared), SHG (second harmonic generation), PFM (piezoresponse force microscopy) and Raman spectroscopy toward the fundamental characterizations of piezoelectric nanofibers are also described. We summarize the report by highlighting recent nanogenerator developments and future prospects including high power nanogenerators, energy storage/regulation systems and fundamentals on piezoelectricity.