The lead-free piezoelectric ceramics (K0.5Na0.5)NbO3 (abbreviated as KNN) with the relative density of 97.6% were synthesized by press-less sintering owing to the careful control of processing conditions. The phase structure of KNN ceramics was analyzed. The results show that the pure perovskite phase with orthorhombic symmetry is in all ceramics specimens. The effect of poling conditions on the piezoelectric properties of KNN ceramics was investigated. The results show that the piezoelectric constant d33 and electromechanical coupling factor kp increase with poling field,poling temperature and poling time increasing,then decrease because of electric broken. Take into account of poling conditions and piezoelectric properties of pure KNN ceramics,the optimum poling conditions for pure KNN ceramics are poling field of 4 kV/mm,poling temperature of 140 ℃ and poling time of 20-25 min.