A food web model is constructed to describe predator-prey interactions, community structure and trophic flows in northern Chile upwelling ecosystem (18°20'S, 24°S), for the year 1997. The model is built using the Ecopath with Ecosim software version 6.4, and encompasses 21 functional groups, ranging from primary producers (phytoplankton) to top predators (birds and marine mammals), the principal fishing resources and the fishery. Input parameters required to build the model were gathered from specialized literature, grey literature and our own estimates. The results indicated that the total biomass (B T) was estimated at 624.7 ton km-2. The combined biomass of small pelagic fish represented 26% of B T, while the combined biomass of demersal fish represented only 0.1% of B T. These results highlight the importance of pelagic fish in this system. Predation mortality resulted to be the main source of mortality. Nevertheless, fishing mortality was important in anchovy, mackerel, common dolphinfish and jack mackerel. The mean trophic level of the fishery was estimated as 3.7, with landings sustained mainly by anchovy. Primary production required to sustain the landings (PPR) was estimated at 7.5% of calculated total net primary production, which is lower than PPR estimates in other upwelling ecosystems. The average trophic transfer efficiency was 18%, which is in the range (10-20%) informed for marine ecosystems. Results indicate that in 1997 the northern Chile marine ecosystem was characterized for being a system far from maturity, dominated in terms of biomass and flows by the pelagic realm.