(K0.5Na0.5)1−xLixNb0.95Sb0.05O3 (KNLNS‐x, x=0–10 mol%) lead‐free piezoelectric ceramics were prepared by the conventional mixed‐oxide method. The temperature stability of the dielectric, piezoelectric, and ferroelectric properties of the two typical compositions (KNLNS‐2 with orthorhombic phase, and KNLNS‐7 with mixed phases) was investigated systematically. The relationship between the orthorhombic–tetragonal polymorphic phase transition (PPT) of the ceramics and the temperature stability of their electrical properties was also discussed. The electromechanical coupling factors (kp and k31) of the ceramics show the maximum values near the PPT, where the temperature stability of the resonance frequency is relatively poor. After the occurrence of the PPT, the remnant polarization (Pr) of the ceramics shows a marked decrease, and a maximum peak in the coercive field (Ec) is observed. Related mechanisms for the temperature stability of electrical properties were also discussed.