Effects of CaCO₃ powder sizes on syntheses and characteristics of CaZrO₃ powders and (Ba,Ca)(Ti,Zr)O₃ (BCTZ) ceramics have been examined in a low-temperature co-firing technique. For the solid state reaction between CaCO₃ and ZrO₂ to synthesize CaZrO₃, the calcination temperature is decreased by applying ultra-fine CaCO₃ powders. Moreover, the lowering of calcination temperature enabled to obtain highly dispersed CaZrO₃ powders with fine grain (80 nm). For the solid state reaction between CaZrO₃ and BaTiO₃ powder, the intermediate products depend on the initial grain size of CaZrO₃ powders (80, 200 and 300 nm), indicating that reaction kinetics is obviously affected by the powder size of CaZrO₃. The dielectric constants of BCTZ ceramics more markedly depend on the CaZrO₃ powder sizes and the reaction behavior between CaZrO₃ and BaTiO₃.