The effect of the mixing quality upon the dynamic response of binary mixtures subjected to low magnitude vibration was investigated. The non-invasive method developed in a previous paper was used to measure the apparent mass as a function of frequency. Horizontally segregated two-phase systems were made by layering the materials. Comparison with well-mixed data showed qualitatively a significant dependence of the apparent mass data upon the quality of mixing, although the quantitative mixing index has not been discussed in this study. The mixing dependence was considered to be attributable to the resonant characteristics of two phases and their interaction effects. Furthermore, the principle was found to be applicable for the monitoring of mixing situations of mixture beds non-destructively and non-invasively. The apparent mass data indicated not only the deviation from an ideal mix, but also the direction of segregation.