The secondary phase compositions in Sb-doped (Ba, Sr)TiO3 ceramics containing SiO2 and excess TiO2 sintering additives have been examined by XRD, BEI and EPMA techniques. It is shown that alongside the primary (Ba0.797Sr0.2Sb0.003)TiO3 phase, (Ba1.95Sr0.05)(2)(Ti1.2Si1.8)O-8 and Sb-doped (Ba0.99Sr0.01)(6)Ti17O40 phases form at the intergranular regions. Substitution of up to 0.04 mol% MnO2 enhances the PTCR effect, giving a ratio rho(max)/rho(min) -7 x 10(5) for the optimum 0.04% MnO2 composition. At this level Mn cannot be detected in the microstructure by EPMA, however in insulating samples containing 0.08 mol% of MnO2, it was detected in the (Ba0.99Sr0.01)(6)Ti17O40 intergranular phase.