Semiconductor particle is attractive material as a photocatalyst in advantage of a large number of reaction sites. Photocatalytic reactions are induced by photoexcited electrons and positive holes, which induce reduction and oxidation reaction on the surface of same particle. Therefore, inverse reaction and recombination are easily occurred compared to electrode reaction system, resulting in largely reducing an efficiency of photocatalytic reaction. In recent years, it is reported that titanium(IV) oxide (TiO₂) consisted of specific exposed crystal-surfaces has higher photocatalytic activity. Electrode experiment of semiconductor single crystal has indicated that photoelectrochemical properties strongly depend on crystal surface. Therefore, different energy levels of conduction and valence band are thought to drive the electrons and holes to different crystal face, leading separation of reaction sites and enhancement of photocatalytic reactions on the TiO₂ particle. In this study, we synthesized anatase TiO₂ particles consisted with specific exposed crystal-surfaces. Titanium(III) chloride and peroxy titanium acid were used as precursor, and they were hydrothermal-treated in the presence of inorganic anion and hydrophilic polymer as controller reagent of exposed crystal-surface. Synthesized particles appeared octahedral or decahedral shape of anatase structure from SEM and TEM observation, and its structure strongly depended on the hydrothermal condition (temperature, hydrothermal reaction time, kind of polymer, pH). Moreover, the TiO₂ particles showed relatively higher photocatalytic activity of acetaldehyde decomposition due to separation of reaction site. Therefore, we carried out further study on relationship between exposed crystal-surface and photocatalytic activity.