Ba0.8Sr0.2Ti1-5x/4NbxO3 ceramics, x = 0, 0.01, 0.05, 0.10, were fabricated by conventional solid-state reaction. With increasing niobium content the ferroelectric phase transition temperature decreases linearly, and the dispersivity of the transition increases. Niobium B-site decreases transition temperature more pronounced than Sr2+ at A-site. The heterovalent substitution of Nb5+ in low content causes local defect dipole, while more substitutions introduce disorder to disturb the long-range dipole correlation. Ba0.8Sr0.2Ti1- 0.5/4Nb0.1O3 ceramic shows weak ferroelectric loop at room temperature far from its transition temperature, 153 K.