Potassium sodium niobate ((K _0.5Na _0.5)NbO ₃)-based lead-free piezoelectric ceramics are excellent ferroelectric materials and have been demonstrated to have many practical applications. Recent studies have revealed that chemical doping plays a crucial role in optimizing the electromechanical coupling properties of (K _0.5Na _0.5)NbO ₃-based piezoelectric ceramics. In this paper, MnO ₂is doped into potassium niobate (KNbO ₃) and (K _0.5Na _0.5)NbO ₃piezoelectric ceramics prepared by the conventional solid-state reaction method. The influences of doped Mn cation on KNbO ₃and (K _0.5Na _0.5)NbO ₃piezoelectric ceramics including microstructure and macroscopic electrical properties are systematically investigated. The doping effects of Mn cation on the KNbO ₃and (K _0.5Na _0.5)NbO ₃piezoelectric ceramics are significantly different from each other. For the Mn-doped KNbO ₃piezoelectric ceramics, the sizes of ferroelectric domains are reduced. Meanwhile, the diffused orthorhombic-tetragonal phase transition is observed, which is accompanied by reducing dielectric loss and Curie temperature, and broadening vibration peaks in Raman spectrum. It is known that the oxygen vacancy can be formed to compensate for the charges created by the acceptor doping of Mn into the Bsite of perovskite, and thus forming a defect dipole with the acceptor center. From the ferroelectric measurement, a double hysteresis loop ( P- Ecurve) and a recoverable electric-field-induced strain due to the formation of defect dipole are observed. On the contrary, for the Mn-doped (K _0.5Na _0.5)NbO ₃piezoelectric ceramics, the sizes of ferroelectric domains are not reduced. Meanwhile, the Curie temperature and vibration peaks in Raman spectrum are not changed. A rectangular hysteresis loop ( P- Ecurve) and an unrecoverable electric-field-induced strain are observed in the ferroelectric measurement. The difference between these systems might originate from the greater ionic disorder and lattice distortion in (K _0.5Na _0.5)NbO ₃piezoelectric ceramics. The difference in ionic radius between Na ⁺and K ⁺can affect the migration and distribution of oxygen vacancies, which makes it difficult to form stable defect dipoles in the Mn-doped (K _0.5Na _0.5)NbO ₃piezoelectric ceramics. The results will serve as an important reference for preparing high-performance (K _0.5Na _0.5)NbO ₃-based piezoelectric ceramics via chemical doping.