β″-Al2O3 has been the dominated choice for the electrolyte materials of sodium batteries because of its high ionic conductivity, excellent stability with the electrode materials, satisfactory mechanical strength, and low material cost. To achieve adequate electrical and mechanical performance, sintering of β″-Al2O3 is typically carried out at temperatures above 1600 °C with deliberate efforts on controlling the phase, composition, and microstructure. Here, we reported a simple method to fabricate β″-Al2O3/YSZ electrolyte at relatively lower temperatures. With the starting material of boehmite, single phase of β″-Al2O3 can be achieved at as low as 1200 °C. It was found that TiO2 was extremely effective as a sintering aid for the densification of β″-Al2O3 and similar behavior was observed with MnO2 for YSZ. With the addition of 2 mol% TiO2 and 5 mol% MnO2, the β″-Al2O3/YSZ composite was able to be densified at as low as 1400 °C with a fine microstructure and good electrical/mechanical performance. This study demonstrated a new approach of synthesis and sintering of β″-Al2O3/YSZ composite, which represented a simple and low-cost method for fabrication of high-performance β″-Al2O3/YSZ electrolyte.