The perovskite-related intergrowth oxides, Sr3-xLaxFe2-yCoyO7-delta (0.3 <= x <= 0.6 and 0 <= y <= 0.6), have been investigated as cathode materials for intermediate temperature solid oxide fuel cells. With a given La content x, the electrical conductivity, oxide-ion vacancy concentration, and thermal expansion coefficient (TEC) increase with increasing Co content y. With a given Co content, while the electrical conductivity increases, the TEC decreases with increasing La content. The electrocatalytic activity and power density measured with Sr3-xLaxFe2-yCoyO7-delta/La0.8Sr0.2Ga0.8Mg0.2O2.8/Ni-Ce0.9Gd0.1O1.95 (GDC) single cells with a GDC interlayer between the cathode and electrolyte increase with increasing Co and La contents due to an increase in electrical conductivity and oxide ion vacancy concentration. The electrical conductivity, TEC, and electrochemical performance of the Sr3-xLaxFe2-yCoyO7-delta cathodes are also compared with those of the LaSr3Fe3-yCoyO10-delta intergrowth and La0.6Sr0.4CoO3-delta perovskite oxides. (c) 2006 The Electrochemical Society.