ABSTRACT A notable diversity of marine mammals inhabits the Atlantic and Pacific waters of South America. For decades, South American countries have been producing scientific research focused on these species. However, still, there is no systematic assessment of the magnitude and main subjects on which this research has been focused. This study analyzes the trends and patterns in scientific research on marine mammals in South America, evaluating a pool of bibliometric indicators and mapping collaborative relationships among countries, authors, and research areas. Academic documents were retrieved from two bibliographic databases: SCOPUS and SciELO, from 1990 to 2020. Results showed a gradual increase in publications along the three study decades. Brazil played a central role in the number of publications in both databases, followed by Argentina and Chile. The South American publications on marine mammals were centralized in a small number of journals, and few authors were responsible for a large proportion of contributions. The authors showed a moderate level of collaboration, mainly reflecting stronger links among neighbor countries, including co-authorships with North American and European countries. The most frequent keywords reflected three clusters centered in taxonomic groups (Cetacea, Odontoceti, and Pinnipedia) and two centered in research subjects (pollution and phylogenetics). The scope of the contributions differed among collections. Nevertheless, both databases were complementary and contributed to show marine mammals' research in South America.