In order to understand how marine ecosystems function, it is essential to study the trophic interactions among the community members, particularly from poorly known regions. In this study, the feeding ecology and diet of conger eels, Conger conger, an abundant fish species with commercial interest, was examined in the north-east Atlantic, off Algarve (southern Portugal) between May 2005 and August 2006. The diet was characterized by species composition, size and mass of prey. Conger eels are opportunistic feeders, cannibalistic, feeding on benthopelagic/pelagic prey (67% by mass and 71% by number) but also benthic prey (32% by mass and 29% by number). Fish (67.8±4.7% in mass) are the main prey of conger eels, followed by cephalopods (16.5±3.8%) and crustaceans (15.6±3.7%). The most numerous (identifiable) fish consumed were Capros aper, occurring in 90% of the stomach samples that contained food and representing 1.4% in mass, and Scomber japonicus, the most important fish in mass (21.1%), which occurred in 4.2% of the stomach samples that contained food. The present study shows that octopodids can play a more important role in the diet of conger eels than previously thought. Of the species preyed upon by conger eels, six species (21% of the total prey taxa) are caught commercially (Trachurus trachurus, Scomber japonicus, Micromesistius poutassou, Helicolenus dactylopterus and Conger conger) by local fisheries. As discards by local trawl and longline fisheries do not correspond with the diet of C. conger, it is likely that most prey of C. conger in rocky areas were caught actively in that study region.