High density (Na1-xKx)NbO3 (x = 0.5, 0.6, and 0.7) ceramics were successfully prepared by spark-plasma-sintering (SPS) method. The dielectric and piezoelectric properties of the SPS samples were investigated and compared to that of hot-pressed samples. It is found that, the SPS-sintered (Na1-xKx)NbO3 samples show higher room temperature dielectric constant, higher coercive fields, lower remnant polarizations and lower electromechanical coefficients than that of the hot-pressed (Na1-xKx)NbO3 samples. The dielectric and piezoelectric property differences between the SPS-sintered and hot-pressed samples have been attributed to grain size effects. (C) 2004 Elsevier Ltd. All rights reserved.