The effects of various dopants including Zr4+, Ce4+ and Ca2+ on the structure and oxygen permeability of B-site doped BaFe0.9Mg0.05X0.05O3-delta (BFM-X) perovskite-type oxygen transport membranes were studied. Slight X cation doping could stabilize the cubic structure of BFM-X perovskite down to room temperature. XRD, SEM and thermogravimetric results revealed that all the cubic BFM-X oxides exhibited good phase stability under argon atmosphere without any phase changes. The weight loss of BFM-Ce from TG analysis suggests the reduction of cerium ions at high temperatures, which may account for its larger electrical conductivity and higher oxygen permeability comparing to BFM-Zr and BFM-Ca membranes. X-ray photoelectron spectroscopy (XPS) data revealed that Ca dopant with larger size caused the mismatch with Fe ions and led to the substitution of Ca ions at both Fe and Ba site in BFM-Ca oxide, being detrimental to electrical conductivity and oxygen permeation. Among these membranes, BFM-Ce has the highest oxygen permeability and good long term permeation stability under air/argon gradient, thus it was recommended as a potential and promising material for air separation.