The utilization of the high-entropy effect and the cocktail effect in high-entropy oxides has significantly expanded the horizon for material design and performance enhancement. Consequently, the fabrication of high-entropy oxides has emerged as a focal point of recent research. High-entropy oxides that serve as cathode materials for battery electrodes must exhibit high electrical conductivity. In this study, a high-entropy oxide (La0.2Ba0.2Cu0.2Sn0.2Ni0.2)3O4 was synthesized using the high-temperature solid-state reaction method. A systematic investigation was conducted to analyze the impact of varying sintering temperatures on the phase structure and electrical properties of the material. The findings indicate that the high-entropy oxide under study possesses commendable electrical conductivity. The electrical conductivity of the material was observed to increase initially and then decrease with the elevation of sintering temperature. Optimal electrical conductivity was achieved at a sintering temperature of 1280 °C. The temperature-dependent electrical conductivity of the sample was found to increase initially and then decrease, with a nominal conductivity of 20.062 S·cm−1 at 25 °C, and a stepwise increase to 30.06 S·cm−1 at 250 °C. This material holds promising potential for applications in energy, electronics, and catalysis sectors.