The authors start, with this note, a systematic study for determination of cestodes of fishes of the Helminthological Collection of the Instituto Oswaldo Cruz. The following species and hosts are refered and described: Schizochoerus liguloideus (Diesing, 1850) and Nesolecithus janicki poche, 1922 both of Arapaima gigas (Cuvier); Gyrocotyle meandrica Herrera, 1946 of Callorhynchus callorhynchus (L.),Acanthobothrium dasybati Yamaguti, 1934 and Pterobothriidae unidentified, of an indeterminate ray; three types of larvae of Trypanorrhyncha and type of Proteocephalidea, of Cynoscion striatus (Cuv.) and C. leiarchus; Proteocephalus jandia Woodland, 1934 of an indeterminate catfish; Monticellia siluri (Furhrmann, 1916) and Amphoteromorphus praeputialis sp. n. of Cetopsis caecutiens and Nomimoscolex magna sp. n. of Pimelodus clarias.