We investigated the piezoelectric properties of a vibration energy harvester using large-area, flexible cantilevers composed of polyurea thin films. The piezoelectric constant d(31) of the polyurea films was measured based on the relationship between the displacement and applied voltage of large-aspect-ratio cantilevers. Centimeter-scale unimorph cantilevers were fabricated, and their energy harvester performance was evaluated by vibrating them. The power generation of the cantilevers with controlled forms was 2.2mV at 50.5Hz (i.e., vibration generation could be efficiently realized at environmental vibrations under 100 Hz).