A new chromatographic method is described for the determination of specific refractive index increment(dn/dc)μ at a constant chemical potential, for polymer/mixed solvent systems. In this method the (dn/dc) is obtained by measuring the areas of solvated-polymer peaks when the mixed solvent is used as an eluent. Values of(dn/dc)μ for the poly(dimethylsiloxane) (PDMS) -benzene-methanol system, determined by the proposed method are in good agreement with those determined by the conventional dialysis method. The new approach has the advantages of simplicity, fast speed, and high reproducibility. The experimental results for stearic acid-chloroform-methanol system show that this method can also be applied to nonpolymer/mixed solvent systems for the determination of (dn/dc)μ.