In this study we emphasize on the role of the geometry upon the magnetic and critical properties of ferromagnetic manganite nanoparticles having stoichiometry La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sub> Ca <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/3</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> . To do that, we consider a set of fine particles of different shapes (spherical and polyhedral) containing approximately the same amount of ions (~8000 magnetic Mn ions) and distributed according to a simple cubic structure. The method is based on the standard Monte Carlo-Metropolis technique. Our theoretical framework employs a classical Heisenberg-like Hamiltonian, where different magnetic nearest neighbor superexchange integrals, preserving orbital ordering for this composition, have been considered. Results showed the specific behavior of the Curie temperature and low temperature coercive force. The studies were done depending on the nanoparticle shapes.