A new nanocrystalline sensitizer with the chemical formula (CH3CH2NH3)PbI3 is synthesized by reacting ethylammonium iodide with lead iodide, and its crystal structure and photovoltaic property are investigated. X-ray diffraction analysis confirms orthorhombic crystal phase with a = 8.7419(2) Å, b = 8.14745(10) Å, and c = 30.3096(6) Å, which can be described as 2 H perovskite structure. Ultraviolet photoelectron spectroscopy and UV-visible spectroscopy determine the valence band position at 5.6 eV versus vacuum and the optical bandgap of ca. 2.2 eV. A spin coating of the CH3CH2NH3I and PbI2 mixed solution on a TiO2 film yields ca. 1.8-nm-diameter (CH3CH2NH3)PbI3 dots on the TiO2 surface. The (CH3CH2NH3)PbI3-sensitized solar cell with iodide-based redox electrolyte demonstrates the conversion efficiency of 2.4% under AM 1.5 G one sun (100 mW/cm2) illumination.