The efficiency of micro-electro-mechanical systems (MEMS) energy harvesters using transverse and longitudinal piezoelectric modes was studied. Since the emergence of piezoelectric MEMS energy harvesters, studies have mainly focused on improving the conversion efficiency at a given strain on a transduction layer. The transverse piezoelectric mode has been applied to use a higher d33 piezoelectric coefficient of a lead zirconate titanate oxide (PZT) material, but few studies have verified its distinguished efficiency compared to that of transverse mode using d31. PZT thin films were deposited on Pt/Ti/SiO2 and ZrO2/SiO2 substrates as the mode by a chemical solution deposition method. The rectangular cantilever with a Si proof mass was fabricated on an SOI wafer, and it has 20 µm of Si device layer. The cantilevered energy harvesters in the same size were respectively fabricated for longitudinal {3-1} and transverse {3-3} mode using parallel electrode plates and interdigitated electrodes (IDE). The generated voltage and power were analyzed considering piezoelectric constants of the PZT films in transverse and longitudinal modes. Since the efficiency of the transverse energy harvester seems to be strongly affected by IDE configuration, a study of this is accompanied. This study might give the direction of choosing the piezoelectric mode for the higher efficiency of MEMS transducers based on the material study.