The electrical conductivity was measured for alpha-Al2O3 powder/various kinds of chloride aqueous solution coexisting systems, and its composition dependence was investigated. We applied the equation of the percolation theory, (sigma/sigma-0) = alpha(phi-1-phi(c))m, (phi-1 > phi(c)), for the purpose of discussion for the composition dependence and tried to give some definitions of the parameters. The composition dependence of the electrical conductivity was influenced by the specific surface area of the solid phase, concentration of electrolyte, and ionic species in the liquid phase. In most cases, because the threshold value, phi(c), was close to zero, the dependence was nearly equivalent to Archie's equation, (sigma/sigma-0) = alpha-phi-1m. For the system containing the powder with large specific surface area as the solid phase, the composition dependence deviated from Archie's equation.