On the North African coast, data on the biology and ecology of the European eel Anguilla anguilla (L., 1758) are very sparse, despite the economic and ecological status of this species. This study aims to collect basic on the fractions of the populations that colonize two transitional waters in eastern Algeria. We provide here the first information on the composition and variations of the diet of A. Anguilla in Mellah lagoon (MLML) and Wadi El Kebir (WEK). During one year (December 2008-November 2009), a total of 1120 eels (NML = 625; 24.3 < TL < 75.8 cm; 23 < TW < 842 g; NWEK = 495; 23.5 < TL < 83 cm; 23 < TW < 1470 g), was sampled. Qualitative and quantitative variations of the diet are looked for in the two sites according to season and development stages. The annual mean values of the coefficient of digestive vacuity were respectively 38.1% and 53.1%. This coefficient varies according to season and development stages. Anguilla anguilla is opportunistic and diversifies its diet between molluscs, teleost fish and Macrophyta, with a preference for crustaceans in the two ecosystems (%IRIML = 89.98%, IRIWEK = 96.15).