The origins of microwave dielectric properties (1 - x)CaTiO3-x(Li0.5La0.5)TiO3 (0.2 <= x <= 0.8) ceramics, prepared by a conventional solid-state reaction method, were investigated based on the theory of bond valence. The XRD and SEM results showed that complete solid solutions with orthorhombic perovskite structure were formed in the whole investigated compositional range. The dielectric constant (epsilon(r)), quality factor (Q x f) and temperature coefficient of resonant frequency (tau(f)) were closely related to B-site, A-site and the difference between A-site and B-site bond valences of ABO(3) perovskite compounds, respectively. As x value increased from 0.2 to 0.8, the dielectric constant increased from 198.3 to 276.8, the Q x f value decreased from 4340 to 1880 GHz, and the tau(f) value varied from +489.7 to -178 ppm/degrees C. For practical applications, excellent microwave dielectric properties of epsilon(r) = 245, Q x f = 2750 GHz and tau(f) = +0.75 ppm/degrees C were obtained for 0.4CaTiO(3)-0.6(Li0.5La0.5)TiO3 ceramics. (C) 2012 Elsevier Ltd. All rights reserved.