We report the synthesis and characterization of BaTiO3 (BT)-based high dielectric compositions that are promising for Y5V-type multilayer ceramic capacitors. A solid solution with a nominal composition (1-x)BaTiO3-xBa(Cu1/3Nb2/3)O-3 (BCN) (x=0, 0.025) was synthesized by conventional mixed oxide route, followed by compositional modification with varying concentration of Sn, as given by the formulation: 0.975 BaTi1-ySnyO3-0.025 Ba(Cu1/3Nb2/3)O-3 (y=0.05, 0.06, 0.075, 0.1). Room-temperature (RT) X-ray diffraction patterns showed a decrease in the tetragonality of BT after modifying with BCN (BTBCN). Modifications with Sn lead to a further decrement in tetragonality and the RT structure became cubic at 6.0 at.% doping level. The decrement in tetragonality was accompanied by lowering of Curie temperature (T-c). BTBCN doped with 6 and 7.5 at.% Sn were found to exhibit diffuse phase transition accompanied by a high dielectric constant >= 7000, a low loss tangent < 1% and a grain size in the submicrometer regime (< 1 mu m).