AbstractDespite the importance of jellyfish in marine ecosystems, many basic biological and ecological aspects remain understudied, especially in tropical regions. Here, we report on scyphozoan jellyfish distribution and ecology to the Amazon coast for the first time, adding the records of Chrysaora lactea, Lychnorhiza lucerna and Stomolophus fritillarius. We also review the records for the three species for the whole Brazilian coastline, describe temporal variability within an Amazon estuary and length–weight relationships. The three species displayed a widespread distribution on the Brazilian coast. In the studied estuary, the species are unevenly distributed throughout the year and their presence was not clearly correlated with environmental factors examined, although L. lucerna is more common during the dry season, as indicated by multivariate and correlation analysis. The length–weight relationships were significant for both L. lucerna (R2 = 0.86, P < 0.0001) and S. fritillarius (R2 = 0.75, P < 0.0001). Jellyfish variability is still unexplained within the estuary despite our 3-year sampling. These jellyfish may be more abundant during the dry season due to the retraction of the amazon plume, but additional sampling designs and methods are needed to test this hypothesis.