The compatibility of SrTi1− x Cox O3 perovskites (0 ≤ x ≤ 0.2) was evaluated for use as interconnect materials in solid oxide fuel cells (SOFCs). Although SrTi1− x Cox O3 perovskites have a single perovskite phase in the range of 0 ≤ x ≤ 0.2, it was observed for SrTi0.8 Co0.2 O3 that Co element agglomerated at the grain boundary during sintering. The dense SrTi0.8 Co0.2 O3 sample was destroyed and included Sr2 TiO4 as a secondary phase after reducing treatment at 1000 °C. As a result of Co doping, the linear thermal expansion coefficient (TEC) increased remarkably with increasing Co content, but the TEC of SrTi0.9 Co0.1 O3 was comparable with those of SOFC cathodes and anodes. Co doping of SrTiO3 effectively increased electrical conductivity in air, whereas the conductivity of Co-doped SrTiO3 in a reducing atmosphere was much lower than that in air. This suggests that the Co ions3+/4+ in the perovskites were earlier reduced into Co2+ ions, compared to Ti4+ ions.