Several specimens of monstrilloid copepods were collected in different localities of Brazil between 1993 and 1997. The taxonomic analysis of these specimens yielded the identification of two new species of Monstrilla. The first one, M. careli sp. nov. can be distinguished by a combination of several characters, including its body proportions, with a very long cephalothorax, by the particularly long terminal segment of the antennules, by the structure of its fifth legs, and by the very long dorsal seta on the caudal rami. The second species, M. brasiliensis sp. nov. can be distinguished by the peculiar features of its fifth leg, with a patch of long and stout hair-like setae along its outer margin; it has also a notched protuberance near the antennule bases. It has a notch on the anterior protuberance of the genital somite, and a ventrally swollen cephalothorax. This species, together with M. inserta Scott bears a pair of enigmatic structures which are either modified sensillae or a vestigial postantennular appendage not previously described in the Monstrilloida.