Crystal structure and dielectric properties of perovskite ceramics in (1 - x)Ba(Ni1/2W1/2)O3-xBaTiO3 (x = 0-0.9) solid solution system have been investigated. The crystal structure of the ceramics changed with the composition of solid solutions. The cubic double pervoskite structure with the space group of Fm (3) over barm was formed for the compositions of x <= 0.15. When 0.45 <= x <= 0.55, the samples had the h-BaTiO3-type hexagonal perovskite structure with the space group of P6(3)/mmc and they changed to the cubic perovskite structure of Pm (3) over bar mas x exceeded 0.7. A cubic-to-hexagonal phase transition occurred in the composition range from x = 0.15 to 0.45. A low-frequency dielectric dispersion was found in the mixed-phase region of double cubic-hexagonal perovskites. A polar cluster model which was responsible for the formation of the hexagonal phase was suggested from a charge-hopping mechanism between B-site cations in the perovskite lattice. This model was then proved by X-ray photoelectron spectroscopy analysis, Raman spectra, and high-resolution transmission electron microscopy observation, respectively. The dense ceramics in the present system with 0.05 <= x <= 0.55 have good microwave dielectric properties with tau(f) of