Lead-free piezoelectric ceramics (1 - x -y)Bi0.5Na0.5TiO3-xBi(0.5)K(0.5)TiO(3)-yBiCoO(3) (x = 0.12-0.24, y = 0-0.04) have been fabricated by a conventional solid-state reaction method, and their structure and electrical properties have been investigated. The XRD analysis shows that samples with y a parts per thousand currency sign 0.03 exhibit a pure perovskite phase and very weak impurity reflections can be detected in the sample with y = 0.04. With x increasing from 0.12 to 0.24 and y increasing from 0 to 0.04, the ceramics transform gradually from a rhombohedral phase to a tetragonal phase and rhombohedral-tetragonal phase coexistence to a pseudocubic phase, respectively. The morphotropic phase boundary (MPB) of the system between rhombohedral and tetragonal locates in the range of x = 0.18-0.21, y = 0-0.03. The ceramics near the composition of the MPB have good performances with piezoelectric constant d (33) = 156 pC/N and electromechanical coupling factor k (p) = 0.34 at x = 0.21 and y = 0.01, which attains a maximum value in this ternary system. Adding content of BiCoO3 leads to a disappearance of the response in the curves of dielectric constant-temperature to the ferroelectric-antiferroelectric transition. The temperature dependence of dielectric properties suggests that the ceramics are relaxor ferroelectrics. The results show that (1 - x -y)Bi0.5Na0.5TiO3-xBi(0.5)K(0.5)TiO(3)-yBiCoO(3) ceramics are good candidate for use as lead-free ceramics.