Mossbauer spectroscopy was carried out for analysis of chemical state of Fe in La1-xSrxGa1-y-zFeyMgzO3-delta system, which attracts interest as new oxide ion conductor operated around 600 degrees C. It was revealed that significant amount of holes were induced by partial Mg substitution for Sr-free LaGa0.8-xFe0.2MgxO3-delta, while large delta can be generated by Sr substitution of La1-xSrxGa0.7Fe0.2Mg0.1O3-delta system. This showed agreement with high oxide ion conductivity and transference number of oxide ion in La0.7Sr0.3Ga0.7Fe0.2Mg0.1O3-delta. (c) 2008 Elsevier B.V. All rights reserved.