Sr- and Mg-doped lanthanum gallate is a well known oxide-ion conductor with potential application in Solid Oxide Fuel Cells operating at intermediate temperatures (500-700oC). One of the main concerns on this solid electrolyte is related to impurity phases, frequently observed even in chemically synthesized powders, due to gallium loss during sintering. La0.9Sr0.1Ga0.8Mg0.2O3-d, LSGM, containing small amounts of Ga2O3 and Sr3Ga2O6 were prepared by solid state reaction, and the effects of the additives on microstructure and ionic conductivity were investigated after sintering at 1350oC. Gallium oxide addition promoted grain growth of LSGM and increased the fraction of the gallium-rich impurity phase. In contrast, strontium gallate addition favored reduction of the fraction of impurity phases. The intragrain conductivity of LSGM increases with gallium oxide addition, whereas strontium gallate improved both the intra- and the intergrain conductivities of LSGM.