The electron transport types and photovoltage gas-sensitive characters of nano-LaFeO3 surface adsorbed by the active gas are probed by surface photovoltage and electric field induced surface photovoltage techniques. The results show that nano-LaFeO3 has the effects of surface and quantum confinement, which results in producing a new surface state band ca. 0.61 eV at the top of the valence band and the photogenic exciton pair in relevant transition. A plot of optimum phase of SPV response versus particle size of the nanocrystalling material is obtained.