A precise value of the third‐order nonresonant susceptibility ratio of carbon disulphide to benzene is determined from coherent anti‐Stokes Raman scattering (CARS) experiments in mixtures of the two liquids. The value is derived from the variation of the frequency separation between the Raman resonance and the interference minimum as a function of the relative concentration of the liquids. The method offers special advantages in many situations of interest.