The feeding habits and trophic level of sea bass (Dicentrarchus labrax) were investigated in the Messolonghi-Etoliko lagoons complex (Western Greece). The stomach content of 570 specimens was examined. Specimens with total length ranging from 17 to 748 mm were collected at monthly intervals during one-year period. Empty stomachs represented 34.5% of the total stomachs examined, showing high seasonal variation (maximum in November: 50%; minimum in May: 12%) as well as variation with size (class total length 17-31 mm: 9%; 141-200 mm: 58%). The most important prey items according to the Index of Relative Importance (IRI), were amphipods (Gammarus sp., IRI= 25.3%), shrimps (Palaemon sp., IRI= 22.5%), crabs (Carcinus sp., IRI= 20.8%), finfish (Atherina boyeri, IRI= 9.9%) and mugilids (Mugilidae) fry and juveniles (IRI= 8.9%) and copepods (IRI= 6.99%). Prey composition shifted progressively with increasing predator size: from small to medium size crustaceans as well as from small and medium size fish like A. boyeri and mugilids young individuals (fry and juveniles). The trophic level of sea bass in the area also increased with predator size ranging from 3 to 4.6. The role of the ecosystem as a nursery and feeding ground for sea bass, as well as the possible trophic competition with other lagoonal species, are also discussed.