The dielectric property of BaTiO3nanoparticles and nanoceramics has been studied on the basis of Ginsburg-Landau-Devonshire thermodynamic theory. In this paper, considering nanodomains, Landau coefficients have been written as a function of grain size, and the dielectric constant of the material has been calculated at a variety of temperatures and grain size. The results indicate that with decreasing grain size, the dielectric peak decreases. The two lower dielectric peaks of the orthorhombic-rhombohedral phase and tetragonal-orthorhombic phase move to higher temperature, while cubic-tetragona...