Surface modification effects have been investigated for perovskite-type mixed ionic-electronic conductors. As the mixed conducting oxides show both ionic and electronic conductivity, these can be applied as oxygen permeable membranes. We have coated surfaces of the perovskite-type mixed conductors, LaSrCoFeO3 and LaSrGaFeO3, with LaSrCoO3 and investigated the effects on oxygen permeability. Enhanced oxygen permeability was achieved when the LaSrGaFeO3 membrane was surface-modified with LaSrCoO3. However, there was no effect on oxygen permeability of LaSrCoFeO3 even when the surface of which was modified. The morphological factors related with electrochemical reactions have also been discussed.