A comparison between the diet of the franciscana and the boto-cinza is presented through the proximate-composition and caloric value of their main prey. The fishStellifercf.rastrifer, Pellona harroweri, Anchoa filifera, Isopisthus parvippinnisandTrichiurus lepturusand the squidsLoligo sanpaulensisandL. pleiwere analysed for water, protein, lipid and mineral contents and gross energy (GE). The fish are more important in the diet of the boto-cinza and squids are consumed mostly by the franciscana.Loligo sanpaulensishad the higher water content and protein was the largest fraction of the organic matter in all prey species. Squids presented greater GE values than fish. The data on prey composition and energy from this study are the first for these South American dolphins.