Dense ceramics with La0.80Sr0.20Ga0.85Mg0.15O2.825 and La0.80Sr0.15Ga0.85Mg0.20O2.825 compositions have been prepared by sintering of mechanosynthesized precursors. The perovskite is synthesized after 85h of milling in a planetary mill. Single phases have been obtained at conditions that are not possible if traditional solid-state reaction (SSR) method is used. The influence of milling time and composition in the reactivity of the precursors is studied. Highest purity is obtained in Sr=0.15 and Mg=0.20 composition, with relative density higher than 97%. The total elimination of typical secondary phases for these compositions, as SrLaGaO4 and SrLaGa3O7, allows the total conductivity of the ceramics to be improved. The influence of the grain size and the nature of the grain boundaries on the electrical characteristic of the ceramics are also discussed.