Nanocrystalline SrTiO3 was prepared by a stearic acid sol-gel technique. X-ray measurements showed that the sample obtained is of good quality and the grain sizes range from 26 to 120 nm. One blue photoluminescence (PL) band at around 470 nm was observed at room temperature. Investigation of the dependence of the visible emission band on annealing temperatures and grain sizes showed that the effects of grain size and dielectric confinement play important roles, and that oxygen vacancies may act as the radiative centres responsible for the observed visible emission band. The mechanism for the luminescence is explained within the framework of self-trapped excitons.