Recently, a new family of piezoelectric perovskite materials based on the solid solution (1-x)BiScO3-xPbTiO(3) was developed. This system was found to have a Curie temperature higher than 450 degrees C and excellent piezoelectric properties near the MPB composition. Niobium, as a donor dopant in the piezoelectric system Pb(Zr,Ti)O-3 and other lead-based perovskite materials, has commonly been used to increase the electrical resistivity, dielectric, and piezoelectric properties. In the current work, the effect of niobium substitution in the BS-PT system has been reported. The results of niobium additions in the BS-PT system showed no large enhancement of the piezoelectric properties. Niobium doping also led to lower Curie temperatures and higher dielectric loss. Further grain size effects in niobium-doped BS-PT compositions provided experimental evidence of significant extrinsic contributions to the piezoelectric properties in this system.