The effect of the structural environment on the Cl- ion conductivity was demonstrated in LaOCl-based solid electrolytes. By replacing the La3+ site with lower-valent Mg2+ or Ca2+ ions, the conductivity was enhanced owing to the formation of a Cl- ion vacancy. Despite the same dopant content, the conductivity of La0.8Ca0.2OCl0.8 was considerably greater than La0.8Mg0.2OCl0.8. This enhancement of the conductivity was influenced by the high ionicity of the Cl- ions, which facilitated the weakening of the La-Cl bond cleavage to conduct inside the lattice. The elongation of the La-La distance, associated with the Cl- ion conduction, could also cause an increase of the conductivity.