The effects of La and Mn dopants on the crystallite growth and the phase transformation of BaTiO3 powders were studied. The barium titanate powders were obtained by calcining barium titanyl oxalate tetrahydrate in the temperature range 800 to 1200 degrees C. Crystallite growth of BaTiO3 powders was promoted by the use of Mn dopant due to the increase of oxygen vacancies. The dissolution of La dopant into BaTiO3 structure may decrease the oxygen vacancies so that the growth of BaTiO3 crystallites is inhibited at high temperature (greater than or equal to 900 degrees C). When the crystallite size is small, the barium titanate can exist as a cubic phase due to the manifestation of the surface energy. Undoped cubic BaTiO3 powders can be stable at a size < 30 nm. Doping with La and Mn would bring the crystallite size for the cubic-to-tetragonal phase transformation to similar to 100 nm, resulting from the presence of cation or oxygen vacancies.