The oesophagus and stomachs of six tucuxi dolphins, Sotalia fluviatilis (Cetacea: Delphinidae) were examined anatomically and microscopically and compared with marine dolphins of the same genus. The oesophagus is a simple distendable tube and is macroscopically uniform to its junctureh with te stomach. This dolphin has a three-compartmented stomach: an anterior or muscular compartment; a principal one, which is glandular; and the pyloric part. The anatomical and functional characteristics of each compartment is described. No sphincter was found between the oesophagus and the stomach. In comparison with marine delphinids there are no adaptations specific to the relatively recent invasion of the fresh-water environment by Sotalia.