Polymer matrix nanocomposites based on polycarbonate (PC) and nanosized-cubic/tetragonal phases of barium titanate (BaTiO3) were fabricated using a solution method followed by hot pressing. The content of both cubic- and tetragonal phased BaTiO3 was varied from 0 to 50 wt%. For a given weight fraction, the dielectric constant of the nanocomposites containing tetragonal BaTiO3 is more than those of cubic BaTiO3 filled nanocomposites. Moreover, cubic BaTiO3/PC nanocomposites showed significantly lower dissipation factor than those of tetragonal BaTiO3/PC nanocomposites. The dielectric constant of the nanocomposites was found to be frequency-independent. The microhardness of the nanocomposites increased with increase in the BaTiO3 content (both cubic- and tetragonal-phased) compared to the pure matrix. Scanning electron microscopy showed better dispersion and good interaction of the tetragonal BaTiO3 nanoparticles in the matrix. The addition of cubic BaTiO3 nanoparticles significantly reduced the thermal stability of the nanocomposites compared to matrix while the addition of tetragonal BaTiO3 nanoparticles decreased it slightly. The glass transition temperature of the cubic BaTiO3/PC nano composites decreased significantly, whereas it reduced slightly for the tetragonal BaTiO3/PC nanocomposites. (C) 2016 Elsevier B.V. All rights reserved.