<p>Piezoelectric nanogenerators (PENGs) transform random biomechanical energy into electrical energy. Beyond improving voltage/current output, a major challenge is enhancing device flexibility, mechanical stability, and biocompatibility. This has motivated the development of polymer composites with piezoelectric particles to overcome limitations of intrinsically piezoelectric materials. This strategy enables novel multifunctional PENGs that combine the biocompatibility and processability of polymers with the piezoelectric properties of fillers. Recent evidence shows that adding conductive nanoparticles to polymer/piezoelectric composites significantly improves output, though without systematic analysis. Conductive particles can modify composite permittivity by altering charge density at polymer/filler interfaces through the Maxwell–Wagner-Sillars effect. They also propagate charges generated on piezoelectric particle surfaces during mechanical stimulation, forming microcapacitors within the PENG. This enhances displacement current from isolated piezoelectric particles, directing charge toward regions that accumulate density at the electrode surface. Additional mechanisms, such as the piezotronic effect, modulating charge transport across metal/semiconductor interfaces under mechanical deformation, may also contribute. This review outlines the fundamental concepts of piezoelectric polymer composites and highlights the overlooked role of conductive particles in enhancing voltage output. Emphasis is placed on their potential to improve ternary PENG designs for biomechanical energy harvesting and to guide future development of high-performance, flexible, and biocompatible energy devices.</p> Graphical Abstract <p></p>