The formation of reverse micelles consisting of a mixture of bis(2-ethylhexyl) phosphoric acid (D2EWPA) and dinonylnaphthalene sulfonic acid (DNNSA) and its effect on the extraction of aluminum and beryllium have been studied. The total concentration of aggregates in the organic phase was measured by the vapor pressure osmometry (VPO) method. The average aggregation number for DNNSA micelle in n-hexane was found to be 16. In the D2EHPA-DNNSA mixed system, the VPO result indicates the existence of dimeric D2EHPA and mixed reverse micelles consisting of both extractants. The mean number of D2EHPA molecules included in a mixed reverse micelle was determined by the relative concentrations of D2EHPA and DNNSA. The contributions of the reverse micelles and dimeric D2EHPA molecules to the extraction of metals were also evaluated. The distribution ratio obtained by the micelles increases substantially through inclusion of D2EHPA molecules into the micelles, with this inclusion causing a synergistic extraction of the metals in the mixed system.