The extraction of Ce(NO3)(3) with N,N'-dimethyl N,N'-dibutyl tetradecylmalonamide (DMDBTDMA) in n-dodecane (0.5M) from acidic (3M HNO3) and neutral (3M LiNO3) media was studied by varying the aqueous cerium concentration up to and beyond the point of third phase formation (defined by the Limiting Organic Concentration or LOC). The acidic system showed better Ce(III) extraction (i.e., a higher distribution ratio, D-Ce), increased water extraction, and also a lower LOC than the neutral system. These observations are consistent with the micellar model, suggesting that acid pre-organizes the organic phase into hydrated reverse micelles that favor Ce(NO3)(3) extraction while increasing the attractive potential between aggregates so that third phase formation happens more readily. The findings in this study underline the importance of aggregation in solvent extraction systems and provide the basis for a wider structural study on the effects of acid on the supramolecular structure of the organic phase.