The genus Micranthocereus includes nine endemic Brazilian species distributed in the states of Bahia, Minas Gerais, Goiás and Tocantins. In the present study the floral biology of M. flaviflorus, M. streckeri and M. purpureus from “campo rupestre” vegetation of the Chapada Diamantina, Bahia, was investigated. Data on floral morphology and nectar production (concentration and volume) were collected throughout anthesis. Flowers of all species are tubular and present coloured perianth-segments. Nectar is accumulated within a nectar-chamber, located inside the floral tube. Flowers of M. flaviflorus and M. streckeri are predominantly nocturnal, opening in the night (at about 7 p.m.). Each flower lasts c.36 hours, with a concentration of sugar in the nectar between approximately 18–24%. Both species present floral features typical for ornithophily, and were pollinated by the hummingbird Chlorostilbon aureoventris, whose visits occurred in regular intervals and were characterized by territorialist behaviour. Species of bees and butterflies were also observed visiting flowers of M. flaviflorus and M. streckeri. M. streckeri was additionally visited by the hummingbird Phaethornis squalidus, mainly in the afternoon. Flowers of M. purpureus are nocturnal, and each flower lasts c.17 hours and present longer corollas with wider diameter than those of the other two species studied; sugar concentration in the nectar was about 21–22%. Three sphingid and one bat species were observed visiting flowers of M. purpureus, with a greater frequency of visits of the sphingids. Pollen viability was high (80–90%) and similar between the three species of Micranthocereus studied.