The present investigation reports a new processing technique that can reduce the sintering temperature of Sr- and Mg-doped lanthanum gallate (LSGM), a good candidate material for the electrolyte of the solid oxide fuel cell (SOFC). When LSGM was sintered at 1623 K for 5 h in N-2 or O-2, the samples were densified over 98% relative density. In contrast, only 93% relative density was achieved after sintering in air, the conventional sintering atmosphere. As a result of better densification in N-2 or O-2, the electrical conductivity of the N-2-sintered and air-annealed or the O-2-sintered sample was higher than that of the air-sintered sample by 30%. This result shows the beneficial effect of N-2 or O-2 sintering of LSGM and provides a high possibility of a low-temperature preparation of an LSGM-based SOFC.