Abstract: The photo-generated carriers properties of TiO₂ nanoparticles annealed at different temperatures have been studied by the field induced surface photovoltage spectroscopy(FISPS) and transient photovoltage (TPV)technique. The transport mechanism of photogenerated electron in bulk phase is different from that in nano-TiO₂ and space charge region of interface of junction. Due to sufficient surface states of TiO₂ annealed under 400 ℃, photovoltage is controlled by the mechanism that photogenerated charge is captured and decaptured by surface states, which is attributed to slow process. After annealed at 800 ℃, the bigger particle is obtained and the energy band has been formed completely. Consequently, except for band-band transition, a band relates to free exciton transition appeared in the band edge in FISPS. The photovoltage is consistent with the direction of external field. The photovoltage is driven by surface built-in field of particles, which is a quick process. While, the powder annealed at 600 ℃, the surface phtovoltage presents the characteristics of homojunction for different crystalline interface. So the low potential barrier presents at interface of anatase phase and rutile phase. The photovoltage is driven by surface built-in field and space charge region of interface of two phases. The photogenerated electron cannot tunnel the interface when it is illuminated by weak light, unless an external electric field is applied.