Lead oxide based ferroelectrics, represented by lead zirconate titanate (PZT), are the most widely used materials for piezoelectric actuators, sensors and transducers due to their excellent piezoelectric properties when their compositions are close to morphotropic phase boundary (MPB). PZT contains more than 60 wt% lead, which is harmful and toxic. There has been a concert effort to develop lead-free piezoelectric ceramics that are biocompatible and environmentally friendly. Lead-free piezoelectric sodium potassium niobate-based ceramics, (Na,K)NbO3, have the potential to replace PZT. Recently, much attention has been paid to the MPB compositions, Na0.5K0.5NbO3 (NKN), to achieve high piezoelectric constants. Lead-free NKN ceramics were fabricated by Spark Plasma Sintering here with the purpose of investigating the effect of grain size (from 0.20 to 0.98 ?m) on domain structures and electrical properties.