In recent years, sodium ion batteries have shown its potential to compliment lithium ion batteries, especially in stationary energy storage system. Additionally, all-solid-state battery is perceived as the holy-grail battery. While numerous research efforts have been devoted to the search of solid-state materials with high ionic conductivity, it is paramount to reduce the thickness of the electrolyte to achieve a high energy density. In this study, the NASICON electrolyte is prepared by tape casting method and its thickness is controlled by the scrapper height during casting. It is realised that the areal specific resistance of the electrolyte is proportional to the thickness of the electrolyte and the 60 μm thick electrolyte shows an extremely low resistance of 42.7 Ω cm². More importantly, such process is highly repeatable for large-scale production of thin freestanding solid-state electrolyte, which can be used in conventional bulk battery, redox-flow batteries, or metal-air batteries.