Piezoceramics because of their electromechanical behavior can be used in many applications such as sensor, actuator and transducer. One of the most important groups of lead-free piezoceramics is based on sodium potassium niobate (KNN) with relatively good piezoelectric properties and high Curie temperature. One of difficulties within fabrication KNN ceramics, which has been postponed their replacement instead of lead-based piezoceramics, is their low sinterability and possibility of alkali elements loss during sintering at high temperatures. Therefore in this study, with the aim improvement of densification behavior of KNN-based compounds, modification and optimization of sintering method were investigated. For this purpose by using solid state reaction, 0.96KNN – 0.04SrTiO 3 powders modified with different amounts (0.0 to 10%) of SrTiO 3 (ST) were prepared and in order to fabricate ceramic samples, sintering was carried out in conventional furnace (either via single step or two-step) as well as microwave furnace. Phase analysis of fabricated ceramics was studied using X-ray diffraction (XRD) and their microstructures were observed by scanning electron microscopy. Dielectric behavior, piezoelectric constant, variation of polarization versus electric field and electric field-induced strain behavior of ceramics were studied. XRD analysis revealed by increasing ST content from 0 to 10%, crystal structure changed from orthorhombic to tetragonal and finally pseudocubic. Density measurement and microstructure investigation of ceramics showed that two-step compared to single step sintering and microwave sintering compared to conventional sintering, decreased sintering temperature, effectively, enhanced densification and improved electric properties. For instant, the maximum piezoelectric constant of single step sintered ceramics was measured 208 pC/N, while by using two-step sintering and microwave sintering it was increased to 278 and 310 pC/N, respectively. The observed improvements of properties were attributed to decrease in alkali elements loss during sintering and reaching finer and more uniform microstructure. The obtained results proved that modification of sintering procedure of KNN-based compounds increase their sinterability considerably and consequently improve their electric properties. Keywords : Piezoceramics; Sintering; Microstructure; Piezoelectricity; Ferroelectric Properties.