The 0.968[(K0.48Na0.52)]Nb0.95+xSb0.05O3-0.032(Bi0.5Na0.5)ZrO3 [KNNxS-BNZ] lead-free ceramics with nonstoichiometric niobium ion were fabricated via conventional solid-state sintering technique and their piezoelectric, dielectric and ferroelectric properties were investigated. When x=0.010, enhanced piezoelectric properties (d(33)approximate to 421pC/N and k(p)approximate to 0.47) were obtained due to the construction of rhombohendraltetragonal phase boundary near room temperature. The KNNxS-BNZ ceramics possesses enhanced Curie temperature (T-c) with improved piezoelectric constant. A large d(33) of similar to 421pC/N and a high T-c similar to 256 degrees C can be simultaneously induced in the ceramics with x=0.010. Especially, good thermal stability was observed in a broad temperature range. The results indicated that our work could benefit development of KNN-based ceramics and widen their application range.