Lead-free piezoelectric ceramics 0.92(Bi0.5Na0.5)TiO3-0.08BaTiO3+xmol% Co3+ (BNBT-Co,x=0-8) are prepared by the solid state reaction method. Effects of the amount of Co3+ on the electrical properties and phase transition are studied. The results indicate that the addition of Co3+ enhances the mechanical quality factor Qm significantly, whereas the dissipation factor tan δ has a minimum value at x=3.5. Meanwhile, addition of Co3+ leads to small decreases of piezoelectric constant d33, and planar electromechanical coupling kp. The present 0.92(Bi0.5Na0.5)TiO3-0.08BaTiO3+3.5mol% Co3+ ceramics exhibit good performance with mechanical quality factor Qm = 910, piezoelectric constant (I33 = 106pC/N, planar electromechanical coupling kp = 10% and dissipation factor tanδ= 1.1% at 1kHz. Saturated polarization hysteresis loops have been obtained for BNBT-Co ceramics. Two dielectric peaks at depolarization temperature Td and Tm appear in the curves of εT33 vs temperature for the pure BNBT ceramics. However, the Grst dielectric peak Td disappears after the addition of Co3+, which means that the transition from ferroelectric to antiferroelectric phase has been eliminated.