In this work, temperature stable microwave dielectric materials (1 − x)AMoO₄–xTiO₂ (A = Ca, Sr) were prepared by a solid state reaction method. The phase composition, sintering behaviors, microstructures, microwave dielectric properties, effective permittivity and vibrational phonon modes were investigated. The X-ray diffraction pattern and scanning electron microscope analysis indicated that the AMoO₄ (A = Ca, Sr) phase could coexist with the TiO₂ phase. The effective dielectric constants of the AMoO₄–TiO₂ composites were calculated by the finite element method (FEM), compared with the measured values and the numerical results obtained by the classical mixing rules. The correlation between the dielectric properties and the crystal structures were studied using IR and Raman spectroscopy. The infrared spectra were analyzed using the classical harmonic oscillator model, and revealed that the external vibration modes of AMoO₄ (A = Ca, Sr) had the most significant influence on the dielectric constant. The Raman spectra showed that there were strong interactions in the [MoO₄] tetrahedron due to the sharp and intense Raman modes. Finally, the low-firing (900 °C) microwave dielectric ceramics were obtained with 3 wt% H₃BO₃–CuO addition (BCu), and they possess good microwave dielectric properties with ε_r = 10.6–13, high Q × f values (40700–72050 GHz), and near-zero temperature coefficients of resonant frequency (TCF or τ_f values). These results also show that (1 − x)AMoO₄–xTiO₂–BCu (A = Ca, Sr) ceramics are good candidates for microwave electronic device applications.