The temperature coefficient of the resonant frequency (TCF) of complex perovskite (Pb1-xCax)[Fe-0.5(Nb1-yTay)(0.5)]O-3 ceramics (x = 0.5, 0.55; 0.0 less than or equal to y less than or equal to 1.0) was investigated, relative to the bond valence of the A- and B-site ions In the ABO, perovskite structure (such as the harium-, strontium-, and calcium-based complex perovskites). The TCF of these complex perovskite compounds varied with the bond valence of the A- and B-sites and the tolerance factor (t) in the perovskite structure. In the tilted region (t < 1.0), the tilting of the oxygen octahedra increased and the TCF decreased, because of the increased bond valence of the B-site, Also, the dependence of TCF on the bond valence of the A-site was similar to its dependence on t.