In most hymenopterans, the ileum extends as a long tube from the midgut to the rectum, and shows no marked anatomical specialization. The function of the ileum is not fully understood, although the presence of an epithelial layer of cuboidal or columnar cells with apical and basal plasma membrane infoldings suggests that this organ may be involved in water and nutrient absorption. In this work, we investigated the ileal morphology of 47 species of bees in the Andrenidae, Apidae (Apini, Meliponini, Xylocopinae, Centridini, Bombini, Eucerini, Euglossini, Tapinotaspidini, Exomalopsini), Halictidae and Megachilidae, as part of a study to understand the physiological and phylogenetic importance of this organ. In all cases, the ileum consisted of an epithelium containing cuboidal or columnar cells that usually had basal nuclei and apical plasma membrane infoldings, although there were variations in cell shape, position of the nucleus, degree of chromatin condensation and cuticle thickness. The epithelial cells were covered with a cuticle and transverse sections revealed the presence of 4-6 folds projecting into the lumen. The cell cytoplasm below the apical plasma membrane infoldings contained numerous vacuoles of different sizes. A single layer of circular muscle was located beneath the epithelium. The histological organization of the ileum suggested a role in the absorption of luminal solutes as a mechanism for regulating the hemolymph and the general osmotic balance of these insects. However, there was no relationship between the structural organization of the ileum and the degree of social development and/or phylogeny of the bees.