Sintered compacts of nano-sized and micron-sized BaTiO3 show sharp ferroelectric transition and high dielectric constant at specific compositions. The sintered compacts with 1 wt% nano-BaTiO3 show a maximum dielectric constant of 1680. At the transition temperature (Tc) there are two maxima at 0.5 and 2 wt%. The variation in the dielectric constant at Tc is also reflected in the behavior of the ferroelectric transition as studied by differential scanning calorimetry. This interesting oscillatory variation of the dielectric constant and dielectric loss with increase in the amount of nanoparticles in the sintered compacts is observed for the first time. The variation of the dielectric properties and the ferroelectric transition of the sintered compacts could be related to subtle changes in the microstructure.