Superfine powders (similar to 100 nm) with compositions of (1 -x)(Bi0.5Na0.5)(0.94)Ba0.06TiO3 + xNb(5+) (BNTBT6 + xNb) with x from 0 to 0.02 were synthesized by an improved citrate sol-gel method using Nb2O5 as Nb5+ source. The sintering behavior, microstructure, and various electrical properties of BNTBT6 + xNb ceramics were investigated. The results indicated that the addition of a small amount of Nb5+ has no remarkable effect on the crystal structure and grain morphology, but the electrical properties of the ceramics are obviously influenced. The BNTBT6 + 0.005Nb compositions exhibit enhanced densification behavior and improved electrical properties of a piezoelectric constant d (33) similar to 205 pC/N and a planar electromechanical coupling factor k (p) similar to 33%.