BaCO3, a common mineral with important applications in industry, has been synthesized in the orthorhombic phase with a high purity. As a new precursor, barium-o-phthalate complex was applied to prepare BaCO3 nanoparticles via solvent-free thermal decomposition route. Thermogravimetric analysis (TGA) was applied to determine the thermal behavior of the complex. The products were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). The best results were obtained for the sample prepared at 500 degrees C. Transmission electron microscopy (TEM) of this product shows "bean-like" shaped nanoparticles with an average size of 35-70 nm. The purity, composition and stoichiometry of the as-prepared sample were studied by Electron Diffraction X-ray spectroscopy (EDX) spectra. (C) 2012 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.