Plastic pollution is a global problem and an improve knowledge in this regard is urgent to find solutions. The aim of this work was to assess, for the first time, the occurrence, types and composition of plastic pollution in juvenile Magellanic penguins (Spheniscus magellanicus) stranded at different beaches from the southern Buenos Aires Province, Argentina. Macro-, meso- and microplastic particles (MPs) were found in 100% of the gastrointestinal tract from 21 individuals. Particle levels ranged from 33 to 200 items per individual. A total number of 1609 particles were extracted and characterized, a 0.2% of particles were macroplastic, 8.8% mesoplastics and 91% MPs, represented mostly by fibers (98.5%). A prevalence of the smallest particles was found (