Rhodnius prolixus is an important vector of Trypanosoma cruzi, the etiological agent of Chagas disease. Insect adults have a pair of Metasternal Glands (MGs) and the secretion emitted by these glands acts as sex pheromone. Recent studies have focused on the chemical composition of this pheromone, electrophysiological responses to MGs compounds and mating behavior assays. Morphological studies of these glands are still scarce. Thus, considering the relevance of MGs in the sex pheromone biosynthesis, we investigated the morphology and ultrastructure of R. prolixus MGs. The glandular apparatus presents a tubular structure containing secretory cells with canalicules that fuse with the central duct which conducts the secretion to a pear-shaped reservoir connected to the exterior by a droplet-shape orifice. The secretory cells are classified as class III, they present a welldeveloped rough and smooth endoplasmic reticulum. Smooth endoplasmic reticulum is a site of lipid biosynthesis that may be involved in the mevalonate pathway, a probable route of the sex pheromone biosynthesis in this insect. The presence of rough endoplasmic reticulum indicates a possible peptides/proteins secretions site which were still not characterized in MGs. Several mitochondria are scattered in the cytoplasm that may suggest a high metabolic activity. Further studies should be carried out to correlate these data with the sex pheromone biosynthesis in this vector.