We developed a three-dimensional spring-type piezoelectric energy harvester using a dip-coating method and multi-directional electrode deposition. The energy harvester consists of a bilayered structure composed of a surface electrode and a ferroelectric polymer, on a conventional spring which has two rolesthe core electrode and the mechanical substrate for the ferroelectric polymer. The energy harvester generated an output voltage of up to 88 mV as a function of cycling compression stress, which leads to a piezoelectric constant of 28.55 pC N 21 for unpoled P(VDF-TrFE) films. Since the spring structure significantly decreases the resonance frequency of the harvester, the springtype energy harvester can effectively generate electricity using low-frequency vibration energy abundant in the nature.Vibration-based energy harvesting (VEH) devices have attracted great interest for use as sustainable and clean electric power supplies for wireless sensor networks that enable health monitoring of important infrastructures such as power plants, bridges and remote power grids. [1][2][3] Since there are abundant vibration sources with a low frequency (between 1 and 200 Hz) in nature, 4 low frequency vibrations are of high interest and are targeted in VEH device design for a wide range of potential applications. [5][6][7][8][9][10] Several approaches exist to convert vibrations to electrical power including electromagnetic, electrostatic and piezoelectric conversion, among which piezoelectric energy harvesting systems (PEHSs) have received the most attention. This is because they directly convert applied mechanical energy into electricity, leading to a simpler device design in comparison to other mechanisms, which require complex geometries and numerous additional components. 1 However, PEHSs are facing challenges such as low output power and high resonance frequency. 8 As the resonant frequency