NaNbO3, one of typical antiferroelectric niobates with a complicated sequence of phase transition, has attracted much attention recently due to its potential application in the energy storage and piezoelectric devices. However, for the traditional ceramic process, it is difficult to prepare uniform and dense NaNbO3 ceramics, affecting its performance optimization. In this work, the sol-gel method in combination with spark plasma sintering (SPS) has been applied to build NaNbO3 fine-grained ceramics. The results revealed that perovskite type NaNbO3 nano-powders with mean size of 40 nm can be synthesized by using an aqueous sol-gel route. Subsequently, using the resulted NaNbO3 nano-powders as precursors, the dense ceramics with mean grain size of 1-2 μm were obtained by SPS method. The electrical measurement evidenced that the defect dipoles play the roles of assisting antiferroelectric to ferroelectric (AFE-FE) phase transition. Moreover, the dielectric constant exhibits good frequency stability and the loss tangent was as low as 0.018 (1 kHz). Our work not only provided the dense NaNbO3 ceramics with potential application in new generational lead-free ferroelectric devices, but also developed a new route to construct fine-grained ceramics, which can be applied to prepare other niobates system.