Ceramics of the series (0.97-x)Bi1/2Na1/2TiO3-xBi(1/2)K(1/2)TiO(3)-0.03NaNbO(3) (x = 0, 0.02, 0.06, 0.10, 0.16, 0.20, 0.30) were prepared by the conventional mixed oxide method. Influence of Bi1/2K1/2TiO3 content on the crystal structure, microstructure, dielectric and piezoelectric properties were studied. All compositions showed single perovskite phase and the morphotropic phase boundary (MPB) between rhombohedral and tetragonal phase existed at the point of x = 0.16. Temperature dependences of permittivity and dissipation factor of unpoled samples revealed that permittivity increased with Bi1/2K1/2TiO3 content and it reached maximum value near the MPB. At the same time, the peak value of dissipation factor increased with the addition of Bi1/2K1/2TiO3. All the samples experienced two phase transitions: from ferroelectric to antiferroelectric at the first transition temperature (T-d) and from antiferroelectric to paraelectric at the temperature (T-m) corresponding to maximum value of permittivity. The phase transition from ferroelectric to antiferroelectric had relaxor characteristic and T-d shifted to lower temperature while increasing Bi1/2K1/2TiO3 content. The best piezoelectric properties were obtained in 0.81Bi(1/2)Na(1/2)TiO(3)-0.16Bi(1/2)K(1/2)TiO(3)-0.03NaNbO(3) ceramic with a piezoelectric constant (d(33)) of 146pC/N, planar electromechanical coupling factor (k(p)) of 30.3% and thickness electromechanical coupling factor (k(t)) of 53.2%. Abnormal piezoelectric properties were observed in the sample (x = 0.20), which was attributed to the co-existence of ferroelectric and antiferroelectric phases in it. (c) 2006 Springer Science + Business Media, Inc.