In this paper the diet of octopus was studied by analyzing the stomach contents of 365 specimens obtained throughout the year from commercial catches. Different prey items, belonging to three taxa (Mollusca, Crustacea and Teleostei) were found, indicating opportunistic feeding behavior. The most important prey species were Callista chione (62.1% IRI, index of relative importance) and Liocarcinos (23.83% IRI). Mollusks (bivalves) were the most frequently found prey group in octopus stomachs according to the index of occurrence and the index of importance in weight and number, followed by crustaceans (brachyurans) and teleosts. The diet was examined in relation to size, sex and seasons. For small O. vulgaris, crustaceans were more important, whereas for larger specimens, bivalves were dominant. The change of the frequency of prey in stomach of octopus by sex and seasons is not significantly different.