© 2022 Elsevier B.V.This study focuses on both synthesis and structural characterization of polycarbazole/barium oxide (PCz/BaO) nanocomposites and the determination of their frequency-based electrical properties such as complex permittivity, tangent loss, and alternating current (ac) conductivity. While PCz was synthesized by using carbazole monomers, BaO nanoparticles (NPs) were obtained by using the co-precipitation method. PCz matrix and BaO NPs were examined by scanning and transmission electron microscopes, X-ray diffraction, and Fourier Transformed Infrared Spectroscopy methods. The electrical properties of the PCz/BaO nanocomposites showed that the energy storage ability of the PCz can be improved with the addition of BaO NPs up to 10 wt% at the low frequencies. Furthermore, the 2.5 wt% BaO NPs contribution causes an increase in ε′ and a decrease in ε'' of PCz. Additionally, it has been determined that BaO NPs doping significantly increases the ac conductivity of the PCz matrix in the low- and mid-frequency regions.