New lead-free bismuth-containing complex perovskite solid solution, (1 - x)(Bi1/2Na1/2)TiO3 - xBi(Mg2/3Nb1/3)O-3, were synthesized by conventional solid state reaction method. Effect of Bi(Mg2/3Nb1/3)O-3 on crystal structure, dielectric and piezoelectric properties were investigated. The XRD analysis showed that all compositions can form single perovskite phase with rhombohedral symmetry. Addition of small amount of Bi(Mg2/3Nb1/3)O-3 improves piezoelectric properties and the optimal piezoelectric properties of d(33)=94 pC/N and k(t)=0.46 were obtained at x=0.7% and x=0.9%, respectively. Temperature dependence of dielectric constant epsilon(r) measurement indicated these compounds were typical relaxor ferroelectric.