The crystal structures and dielectric properties of the (1-x)Ca(Mg1/2W1/2)O-3-xCaTiO(3) solid-solution system are investigated. This solid solution system is single phase of perovskite-type structure in the whole composition range. It has been found that the Ti4+ ions almost equally substitute Mg2+ and W6+ site, not disturbing chemical ordering between Mg2+ and W6+. This distinctive feature of substitution results in volume difference between the MgO6 and WO6 octahedra. Consequently, the crystal system changes from the monoclinic to orthorhombic with increasing Ti4+ substitution. Moreover, the relatively small Ti4+ substitution continuously decreases the unit cell volume. The structural changes are responsible for the temperature coefficient change of dielectric constant (tau(epsilon)) which monotonically decreases with increasing x. The dielectric constant (epsilon(r)) increases rapidly with increasing x. The relationship between crystal structures and dielectric properties is presented.