We have investigated the influence of the excess doping of alkaline earth oxides on the structure and electrical conductivity of the Ba_xSr_yLa_0.50InO_2.25+x+y (x+y≧0.5) system. It was found that over 0.10 mol of BaO or SrO could be doped in 1 mol of the cation stoichiometric system (x+y=0.50). We propose that some of the Sr cation move from A-sites to B-sites in this system to maintain the cation stoichiometry [(x+y+0.50) : In=1 : 1]. The dependence of the electrical conductivity on the oxygen partial pressure varied with the magnitude of the oxide ion conductivity. The oxide ion conductivity of the excess-doped system was dependent on the unit cell free volume. The relationship corresponded to that of stoichiometric Ba_xSr_yLa_0.50InO_2.25 (x+y=0.50) and Ba_1-yLa_yInO_2.50+y systems.