Single phase of Ba1-xLaxFeO3-delta (x = 0.1-0.6) with cubic perovskite structure and random arrangement of oxide ion vacancy was successfully prepared by sintering under N-2 flow whose P(O-2) was approximately 10(-4) bar. It was revealed that chemical state of Fe was almost 3.0 + at room temperature regardless of La content, resulting in decrease of delta from 0.48 to 0.26 with increasing La content from 0.1 to 0.5. High temperature X-ray diffraction measurements indicated stability of the cubic structure from room temperature to 1000 degrees C under P(O-2) of 10(-2) bar. Electrical conductivity increased with increasing La content up to log (sigma/S.cm(-1)) of about 1.5 for Ba1-xLaxFeO3-delta, indicating high potential as electron and oxide ion mixed conducting material. The variation of electrical conduction behavior from semiconducting to semi-metallic and discontinuous variation of thermal expansion behavior at 300-400 degrees C under P(O-2) of 10(-2) bar could be attributed to abrupt oxygen uptake as large as Delta delta = 0.185 at the temperature. The decrease of electrical conductivity with increasing temperature and deviation of linear thermal expansion above 400 degrees C could be ascribed to increase of delta above 400 degrees C.