Amazonian flooded (várzea) and upland (terra firme) forests harbor distinct assemblages of most taxonomic groups. These differences are mainly attributed to flooding, which may affect directly or indirectly the persistence of species. Here, we compare the abundance, richness and composition of butterfly assemblages invárzeaandterra firmeforests, and evaluate whether environmental gradients between and within these forest types can be used to predict patterns of assemblage structure. We found that both total abundance and number of species per plot are higher invárzeathan interra firmeforests.Várzeaassemblages had a higher dominance of abundant species thanterra firmeassemblages, in which butterfly abundances were more equitable. Rarefied species richness forvárzeaandterra firmeforests was similar. There was a strong turnover in species composition fromvárzeatoterra firmeforests associated with environmental change between these forest types, but with little evidence for an effect of the environmental gradients within forest types. Despite a smaller total area in the Amazon basin, less defined vegetation strata and the shorter existence over geological time of floodplain forests, Nymphalid-butterfly assemblages were not more species-poor invárzeaforests than in unflooded forests. We highlight the role of flooding as a primary environmental filter in Amazonian floodplain forests, which strongly determines the composition of butterfly assemblages.