Undoped and Nb-doped SrTiO3 specimens with excess titania compositions were prepared by sintering in air at 1420 or 1480 degrees C. Large grains due to liquid-phase sintering were obtained for undoped specimens containing greater than or equal to 0.6 mol % excess titania and fired at 1480 degrees C. On the other hand uniform fine grains were observed for samples fired at 1420 degrees C, resulting from grain-growth inhibition due to exsolved TiO2 second phase. The solubility of excess titania seemed less than 0.2 mol % under our experimental conditions. The microstructural behaviour of Nb-doped SrTiO3 could be explained well by the Sr-vacancy compensation model. According to this model, the solubility of excess titania in SrTiO3 increased with Nb2O5 dopant concentration. Thus, for Specimens which had high excess titania compositions and were sintered at 1480 degrees C, large grains were observed when the Nb content was low enough to retain sufficient excess titania-forming liquid phase. For specimens having the same compositions and fired at 1420 degrees C, uniform fine grains were obtained due to grain growth inhibition by the exsolved TiO2 second phase, when the Nb content was low. If the excess titania was less than the solubility determined by the amount of Nb dopant, Ruddlesden-Popper-type phases were believed to be formed and resulted in poor densification. Although excess titania was the major factor in determining the grain size of the specimens, the niobium dopant enhanced grain growth.