An empirical relation for the relative permittivity in quarternary III-V semiconductor compound is suggested as a function of composition. The expression for the permittivity of ternary III-V compounds can be obtained from that as a special case which is identical to that already available in the literature. Graphs have been plotted for static and optical permittivities against composition for the quarternary semiconductor In//1// minus //xGa//xAs//yP//1// minus //y and are discussed.