The pseudocubic structure of a (Na0.5K0.5)NbO3 (NKN) film grown on a Pt/Ti/SiO2/Si substrate changed to an orthorhombic structure when the film was transferred onto a polyimide substrate. Piezoelectric constant for the transferred NKN film increased considerably from 74 ± 11 to 120 ± 18 pm/V because the crystal structure of the film had changed from pseudocubic to orthorhombic. A gold interdigitated electrode was deposited onto the transferred NKN film to synthesize a NKN piezoelectric energy harvester. The NKN piezoelectric energy harvester was poled before bending under a 100 kV/cm DC electric field across the electrodes. When a strain of 0.85% and a strain rate of 4.05%/s were applied to the NKN piezoelectric energy harvester, it produced a maximum output voltage of 1.9 V and a current of 38 nA, corresponding to a power density of 2.89 μW/cm3.