Lead-free piezoelectric ceramics have received more attention due to the environmental protection of the earth. Niobate ceramics such as NaNbO3 and KNbO3 have been studied as promising Pb-free piezoelectric ceramics, but their sintering densification is fairly difficult. In the present study, Spark Plasma Sintering (SPS) was applied to the sintering of Na0.5K0.5NbO3 ceramics, whose powder was synthesized by the conventional oxide mixing method. No loss of sodium and potassium were found in the SPS sintering process, by which the density of the K0.5Na0.5NbO3 solid solution ceramics was raised to 4.21g/cm3 (>93% of the theoretical density) at temperatures as low as 920°C. The crystal phase of the Na0.5K0.5NbO3 is an orthorhombic structure. The piezoelectric parameter (d33) of the K0.5Na0.5NbO3 ceramics reached 49 pC/N.