Monodispersed barium zirconate (BaZrO3) fine particles with a spherical shape have been synthesized by hydrothermal reactions using barium hydroxide and a Zr-triethanolamine (TEOA) complex. The particle mean diameter was gradually controlled in a range from 0.20 mu m to 3.5 mu m by change in the added amount of seed nanoparticles. The mechanistic characterization of the seed-mediated BaZrO3 sphere synthesis revealed that the particle growth obeyed a simple seed growth mechanism. In the present system, utilization of the Zr-TEOA complex played an important rule to prevent uncontrollable nucleation to form the uniform BaZrO3 fine particles with narrow size distributions. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.