A new microfossil association was found in the Allen Formation at Loma Puntuda (Neuquen Basin, Rio Negro Province, Argentina). It is represented by scarce charophyta and numerous carapaces and valves of ostracods from the families Ilyocyprididae (such as Ilyocypris riograndensis and several species of Neuquenocypris) and Limnocytheridae (with the species Wolburgiopsis neocretacea and Vecticypris sp.). Molluscs, fragments of dinosaur eggshells and a plesiosaur remains had been registered previously in the same profile. This kind of association of non marine with a few marine fauna seems to indicate that the Allen Formation at Loma Puntuda was deposited in a shallow, fresh to oligohaline water body, near the coast. © 2011 by the Sociedade Brasileira de Paleontologia.