Lanthanum molybdenum oxide, La2Mo2O9 has been well studied since the first report of its high oxide ionic conductivity in the year 2000. In this work effect of different alkaline earth (namely Ba, Sr and Ca) substitutions in low concentrations on structure and ionic conductivity of La2Mo2O9 has been investigated. All the substituted (3, 5 and 8 mol%) compositions synthesized instantaneously by a citrate-nitrate auto-ignition process. The synthesized materials have been characterized by thermal analysis, X-ray diffraction and impedance spectroscopy. 3 mol% Ba+2 substitution has been found to be enough to stabilize high temperature beta form but for Sr+2 substitution, minimum concentration required to stabilize the beta form has been detected as 8 mol% and for Ca+2 even 8 mol% has found to be not sufficient enough. A conductivity maxima has been shown Ba substitution at 3 mol% but for Sr+2 and Ca+2 such phenomenon has not been detected. The 3 mol% Ba+2 substituted composition has shown the highest electrical conductivity among the all the studied compositions and it has been found to be predominantly ionic. (c) 2012 Elsevier B.V. All rights reserved.