The ultrasonic velocity of the solutions of iron (III) soaps (Caprate, Laurate and Myristate) were carried out in a mixture of benzene and methanol (50:50 v/v) at a constant temperature. The data obtained have been used to evaluate the critical micelle concentration (CMC) and to study the soap-soap and soap – solvent interactions. The various acoustic parameters, viz adiabatic compressibility, intermolecular free length, apparent molar compressibility, specific acoustic impedance, molar sound velocity and solvation number were evaluated. The results show that the values of CMC are in agreement with the values obtained from other micellization properties.