The response of a phase Doppler instrument has been predicted for the sizing of evaporating multicomponent droplets. This study uses the theoretical model of Schneider and Hirleman  and extends its application to droplets consisting of liquid mixtures. The results obtained for binary heptane/dodecane droplets are discussed for different scattering angles. The internal refractive index gradients considerably affect the relation between phase difference and droplet diameter at mean scattering angles of Θ = 30° and Θ = 160°. However, the absolute variations of the calibration curves are smaller compared to those observed for a single component droplet. Additionally a mean scattering angle of Θ = 70° has been investigated. These results clearly demonstrate the insensitivity of the Θ = 70° scattering configuration on internal refractive index variations and thus confirm the recommendation of Pitcher et al.  ,who considered minimizing errors due to unknown but homogeneous refractive indices.