Nano-grained BaTiO3 ceramics prepared from 40 nm size BaTiO3 nano-powders exhibited the cubic as well as the tetragonal phase, while the nano-grained BaTiO3 ceramics prepared from the BaTiO3 nano-powders coated with Mn had only the tetragonal phase. The variation of phase transition of the BaTiO3 ceramics appeared to be significantly affected by the grain boundary features; the effect of the grain boundary features resulted in the phase transition from the cubic to the tetragonal phase in the nano-grained BaTiO3 ceramics, even though the grain size was about 40 nm. The chemical origin of the effect of grain boundary on the phase transition of the nano-grained BaTiO3 ceramics was strongly suggested. (c) 2004 Elsevier B.V. All rights reserved.