We have stabilized the perovskite La 2/3 TiO 3 by adding LaFeO 3 and shown that in general the stabilization mechanism for the (1−x)La 2/3 TiO 3–x LaFeO 3 mixture involves the formation of a solid solution for compositions with x≥0.04. The crystal structure of the solid solution transforms from orthorhombic to tetragonal at x=0.2, becomes cubic in the range 0.3<x<0.8, and transforms again into orthorhombic (typical for pure LaFeO 3 ) for values greater than 0.8. Detailed impedance-spectroscopy measurements for various compositions and conditions showed that the limiting step in the conduction mechanism was conduction across the grain boundaries. In the concentration range 0.04<x<0.25 the room temperature conductivity increases up to 0.0017Scm −1 , after which it decreases again. Part of the initial increase is probably due to the formation of free electrons in accordance with (Fe Ti )′→(Fe Ti ) x +n′. Other defect-formation mechanisms are also discussed, but are ruled out for a variety of reasons. Another interesting phenomenon that also affected the average conductivity was identified, i.e., the variation of the average particle size with composition.