Lead-free relaxor ceramics with composition (Na 0.5K 0.5) 1−3 x La x Nb 0.95Ta 0.05O 3 (KNTN-La x ) were prepared by the conventional solid-state route. The ferroelectric relaxor behavior and dielectric properties of KNTN-La x ceramics were systemically investigated. X-ray diffraction analysis showed that the crystal structure of the ceramics changed from orthorhombic to pseudo-cubic with increasing La-doping level. Dielectric study revealed that KNTN-La x ceramics underwent a transition from a normal ferroelectric to relaxor-like ferroelectric. Furthermore, P– E hysteresis loops, which were of slim-loop type with small remnant polarization values in the composition range of 0.015 ≤ x ≤ 0.03 confirmed the ferroelectric relaxor behavior of KNTN-La x ceramics. The samples of KNTN-La x ceramics in the composition range from x = 0 to 0.015 exhibited good electrical properties, piezoelectric constant d 33 of 98–119 pC/N and electromechanical coupling coefficients k p of 33.2–37.0%, respectively. The results show that the series of KNTN-La x ceramics is one of the promising lead-free materials for electromechanical transducer applications.