We present data on nests of the two species of the neotropical bee genus Ananthidium Urban (Megachilinae, Anthidiini). Five nests of Ananthidium dilmae Urban, a species from southern and southeastern Brazil, were found in grassland areas at the Vila Velha State Park, Ponta Grossa, in Paraná State. The aerial nests were made of resin mixed with plant fibers and each contained one or two cells. One female and one male emerged from two of the nests. Notes on the nest of Ananthidium inerme (Friese), a species known from Argentina and Paraguay, are provided based on two nests deposited in Berlin’s Museum für Naturkunde, Germany. This species also builds aerial resin nests attached to plant stems, with external shape and dimensions similar to those of Ananthidium dilmae.