To investigate the donor segregation in grain boundary regions and its effect on grain growth in SrTiO3, SrTiO3 powder compacts were doped with Nb2O5, and sintered in air or in hydrogen. The Nb-doped SrTiO3 sintered in air did not show any detectable Nb segregation at the grain boundary region while an appreciable segregation was observed in the space-charge region of the sample sintered in H-2. The observed donor segregation in H2 suggests a negative grain boundary charge and compensating positive space charge, which are the opposite to those in air. The negative grain boundary core was attributed to the segregation of inherently present acceptor impurities and the trapping of electrons at grain boundaries. In the H-2-sintered sample, where the added Nb ions were segregated in the space-charge region, the grain growth was suppressed. This result may indicate that the grain growth suppression in H2 is due to the Nb solute drag of the boundary motion and the reduction in Ti vacancies.