BaTiO3 nanoparticles with excess barium are directly synthesized from solution at 65 degrees C. It is noted that a small amount of BaCO3 exists in the as-prepared samples. A series of standard mixtures with different proportion of BaTiO3 and BaCO3 are measured by XRD analysis to quantify the amount of BaCO3 in our synthesized samples. After a deduction of the amount of BaCO3, the concentration of excess barium in the lattice of BaTiO3 nanoparticles can be determined and the results show that the excess barium can reach a considerable concentration. The influences of defects and surfaces on BaTiO3 nanoparticles with excess barium are analyzed and two important reasons for the high concentration are also given. (c) 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.