We propose a spiral-shaped piezoelectric bimorph power harvester operating with coupled flexural and extensional vibration modes for applications to low frequency energy sources. A theoretical analysis is performed and the computational results show that the spiral structure has relatively low operating frequency compared to beam power harvesters of the same size. It is found that to optimize the performance of a piezoelectric spiral-shaped harvester careful design is needed.Keywords: spiral-shaped bimorph, piezoelectric harvester, power density.Piezoelectric materials have been used for a long time to make various electromechanical transducers. In particular, due to their strong piezoelectric coupling, polarized ferroelectric ceramics have been used for force or power handling devices including actuators and transformers, etc. Recently, due to the rapid development of wireless electronic devices in both civilian and military applications, operating some of these devices without a wired power source has become an important issue. One approach is to harvest power from the operating environment [1] . Piezoelectric materials are natural candidates for designing devices that scavenge ambient power by converting mechanical energy into electric energy [1][2][3] for powering small electronic devices of a very low power requirement. Such a piezoelectric device, termed as a piezoelectric generator or power harvester, can be viewed as one half of the structure of a piezoelectric transformer [4][5][6] in which the energy converts twice, i.e., from electrical to mechanical and then from mechanical to electrical.A piezoelectric power harvester is a resonant device operating at a particular frequency. The energy sources, e.g., noise or mechanical vibration, from which a harvester can pick