The diet of the Sanderling (Calidris alba) was studied using 105 droppings, 34 pellets and direct observations of feeding behavior. This study was carried out during the non-reproductive seasons of 1996 to 2000 in Monte Hermoso, SW of Buenos Aires, Argentina. A total of eleven prey items were identified, with beetles (Coleoptera), Mussels (Brachydontes rodriguezi), clams (Corbula sp.), amphipods (Corophium sp.) and Diptera being the most frequent. The consumption of polychaetes, algae, ants and small fish was also recorded. Sanderlings followed foraging American Oystercatchers (Haematopus palliatus) and cleaned out the valves of mussels and clams (Mesodesma mactroides) left by them. Mussels and beetles were the most constant and dominant prey during the study period. The association of Sanderlings with sandy coasts with rocky patches or restingas is probably due to the rich and diverse invertebrate communities present in this kind of environment, which allow birds to change feeding techniques between different substrates.