<p>Bamboo density is a primary driver of changes in vegetation structure in the southwestern Brazilian Amazon, also affecting the forest litter, a significant and diverse component of which is ants. Here, we investigated the impact of bamboo dominance on litter ant assemblages with the following hypotheses: (i) bamboo patches have a more homogeneous and denser litter layer, (ii) which reduces the number of ant species, (iii) alters species composition, and (iv) results in smaller body sizes and simpler structures in litter ants. Additionally, bamboo patches are expected to have (v) a more open canopy, leading to (vi) a higher number of generalist and open-habitat specialist species compared to forest specialists. To test these hypotheses, we established 30 paired plots along the boundary between bamboo and non-bamboo habitats in an Amazon Forest fragment in Acre, Brazil. In each plot, we collected a 1 m² sample of the litter layer for ant sampling using a mini-Winkler extractor. We also measured litter density, litter heterogeneity, and canopy openness in each plot. Our findings showed that bamboo habitats present less dense litter layers, that heterogeneity did not differ, a higher number of ant species, and smaller ants. Species composition weekly differed between the habitats. In conclusion, the dominance of bamboo primarily affects ants through morphological filtering rather than species composition. Given that climate and land-use changes may promote the expansion of bamboo patches in the region, this could have significant impacts on ant assemblage composition and their ecosystem functions.</p>