Effect of sintering, between 550 and 950 °C, on dielectric properties of ceramic composite BaO:ZnO (BZO) was investigated in a low radio frequency range of 0.0–2.0 MHz. BZO ceramic composite was prepared by the facile autocombustion synthesis method. BaO and ZnO crystallized into tetragonal and hexagonal structures, respectively, coexist as an agglomerated microstructure inside the BZO composite. UV–Vis DRS, FTIR, photoluminescence and Raman spectroscopy were employed to find band gap energies, functionalization groups, excitation wavelength and the presence of vibrational modes of the sintered BZO composites. Scanning electron microscopy sufficed agglomerated structure of increasing particle size with temperature. Dielectric analysis showed that the maximum dielectric constant of 1.8 was observed for the composite sintered at 550 °C and then it decreased after heating at 650 °C. On further heating, an increase was observed in the dielectric constant of the BZO till 950 °C. The initial decrease was attributed to the presence of residual Ba(OH)2 phase. The loss tangent was reduced from 0.6 to 0.02 due to the post-synthesis sintering process. The sintered BZO exhibited increase in conductivity and decrease in resistivity in 0.0–2.0 MHz range. Similarly, the overall decline in real and imaginary permittivity was noticed with a uniform trend in the limit of 0.5–2.0 MHz. An increase in crystallite size from 41.36 to 92.54 nm for BaO and 22.23 to 40.99 nm for ZnO affected the dielectric constant. First, it decreased after heating at 650 °C and then increased up to 950 °C. During heating, a decrease in the interfacial polarization and an increase in the ionic polarization were attributed to the inter- and intra-crystallite boundary variations that played a role in the overall dielectric character of the BZO. The stability of dielectric parameters in the 0.25–2.0 MHz range suggested tuning these quantities by simply sintering process.