(1-x)K0.5Na0.5NbO3-x(0.97BiScO3-0.03BiCoO3) (KNN-xBSC) piezoelectric ceramics were prepared by the conventional solid-state method, and effects of the BSC addition on the phase structure, relaxor behavior, and electrical properties of KNN ceramics were systematically investigated. The rhombohedral to orthorhombic phase transition around room temperature was identified for the KNN-xBSC ceramics in the composition range of 0.015≤ x ≤0.0175, and improved electrical properties (d
33∼205 pC/N, k
r∼1315, and tan δ∼0.054) were observed for the ceramic with x=0.015 because of the involvement of such a phase transition at room temperature. Moreover, a relaxor ferroelectric behavior is demonstrated for these KNN-xBSC ceramics because of a more complex occupation of A and B sites in the ABO3 perovskite structure, together with a weak ferromagnetic order at room temperature.