Copepod grazing impact on planktonic com- munities has commonly been underestimated due to the lack of information on naupliar feeding behaviour and ingestion rates. That is particularly true for small cyclopoid copepods, whose nauplii are mainly in the microzoo- plankton size range (<200 lm). The trophic role of Oithona spp. nauplii was investigated off ConcepcioŽ n (central Chile, *36°S) during the highly productive upwelling season, when maximum abundances of these nauplii were expected. Diet composition, ingestion rates, and food-type preferences were assessed through grazing experiments with different size fractions of natural plank- tonic assemblages (<3, <20, <100, and <125 lm) and cultures of the nano&#64258;agellate Isochrysis galbana. When the Oithona spp. nauplii were offered a wide range of size fractions as food (pico- to microplankton), they mostly ingested small (25 µm) nano&#64258;agellates (563 x 10^3 cells nauplius^-1 day^-1). No ingestion on microplankton was detected, and picoplankton was mainly ingested when it was the only food available. Daily carbon (C) uptake by the nauplii ranged between 28 and 775 ng C nauplius^-1, representing an overall mean of 378% of their body C. Our relatively high ingestion rate estimates can be explained by methodological constraints in previous studies on naupliar feeding, including those dealing with over-crowding and edge effects. Overall, the grazing impact of the Oithona spp. nauplii on the prey C standing stocks amounts up to 21% (average = 13%) for picoplankton and 54% (average = 28%) for nanoplankton. These estimates imply that the nauplii of the most dominant cyclopoid copepods exert a signi&#64257;cant control on the abundances of nano- plankton assemblages and, thereby, represent an important trophic link between the classical and microbial food webs in this coastal upwelling system.