Oxide ion-conducting materials have captured much research interest due to their use in various electrochemical devices such as SOFCs, oxygen sensors, separation membranes and oxygen pumps. Recently, a few hexagonal perovskite materials' systems show good oxide ion conductivity in wide range of oxygen partial pressure. Here, we have synthesized the a recently explored oxide ion-conducting hexagonal perovskite-based system Ba3MoNbO8.5 via solid-state reaction route and investigated its structural, microstructural and most importantly electrical properties for its suitability as solid electrolyte in electrochemical applications. Rietveld refinement of X-ray diffraction pattern of calcined powder of Ba3MoNbO8.5 was carried out to check the required phase formation. Refinement of XRD data reveals the hexagonal symmetry phase having R 3 ¯ mH space group. FT-IR, Raman and UV spectroscopy measurement were performed to find the crystallographic orientation, vibrational/rotational modes and band gap of the materials. SEM–EDX study was performed to perceive the morphological behavior, densification and chemical composition of constituents. The electrical conductivity of the system was measured using impedance spectroscopy technique and found to be ~ 0.16 × 10–2 Scm−1 at 650 °C. A predominant two-dimensional oxide ion migration was found via the BVE analysis of crystallographic data of the investigated system suggests oxide ion conductivity in the system. [ABSTRACT FROM AUTHOR]