Ce0.8Nd0.2O1.9 (NDC) and La0.95Sr0.05Ga0.9Mg0.1O3-δ (LSGM) electrolytes were each prepared using a sol-gel method. NDC-LSGM composite electrolytes were then prepared by adding 0-15% (w, mass fraction) precalcined LSGM powders to NDC sols. The microstructure and phase composition of the pellets were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and energydispersive X-ray spectroscopy (EDS). The electrical conductivities of the pellets were measured using alternative current (AC) impedance spectroscopy. The results showed that all the composites were composed of the cubic fluorite structure, perovskite structure, and secondary phases. The LSGM additive significantly promoted grain growth. The grain boundary conduction increased greatly as a result of the presence of phase interfaces and mitigation of the harmful effects of SiO2 impurities. NL10 was found to have the highest conductivities (σgb=12.15×10-4 S·cm-1, σt=3.49×10-4 S·cm-1 at 400 ); these values are 7.62 and 1.91 times higher than those of NDC (σgb=1.41×10-4 S·cm-1, σt=1.2×10-4 S·cm-1). The enhancement of the total conductivity of NL10 is mainly attributed to the large increase in grain boundary conductivity.