As a lead-free piezoelectric material, (K,Na)(Nb,Ta)O₃(KNNT) ceramics were synthesized by the solid state reaction method. Although KNNT ceramics were sintered by hot pressing due to the difficulty in normal sintering, the sinterability of this ceramics was greatly improved by the sintering aid ((K₄CuNb₈O₂₃ or K_5.4Cu1_1.3Ta₁₀O₂₉). With the increase of sintering aids, dielectric constant and Curie point changed lineally. This result means that a part of KCN or KCT react with KNNT and form a solid solution with KNNT. In addition, in order to improve the temperature properties, Li substitution for A site ions was investigated. 4 mol% Li substituted sample showed 50C higher Curie point than pure KNN ceramics.