This study was carried out to examine histological and enzyme histochemical characteristics of the oesophageal tonsil in ducks (Anas platyrhynchos). Tissue samples were collected from distal parts of the mucosal folds at the oesophagealyproventricular junction. We applied alpha naphthyl acetate esterase and acid phosphatase to tissue sections for localisation of T or B lymphocytes. Trichrome staining, silver impregnation, methyl green-pyronin staining and PAS reaction were used for determination of light microscopic structure of the oesophageal tonsils. The oesophageal tonsils were located at the junction of the oesophagus and proventriculus. Interestingly, we detected the existence of high endothelial venules in the interfollicular area and of the accumulated positive cells in lymphoid nodules. It can be said that these tonsils have functions similar to the Harderian gland in avian species and Waldeyer's ring in mammalian species.