One hundred specimens of unicorn leatherjacket, Aluterus monoceros purchased from markets of municipalities of Niterói and Rio de Janeiro from May to August 2006. The fishes were measured, necropsied, fileted and analysed their organs. Sixteen fishes were parasitized by nematode Anisakidae: Anisakis spp. and Contracaecum sp. with respectively, 1 and 16% of prevalence, 2 and 3.31 of mean intensity, and 0.02 and 0.53 of mean abundance. Two larvae of Anisakis sp. were found in mesentery of one fish and Contracaecum sp. was found in liver and mesentery with 1 to 9 specimens of range of infection. Fifty-one fishes were parasitized on the liver and mesentery by metacestodes of Trypanorhyncha. The collected species were Floriceps saccatus and Callitetrarhynchus speciosus with respectively, 45 and 6% of prevalence, 3.17 and 2.83 of mean intensity, and 1.43 and 0.06 of mean abundance, the range of infection by F. saccatus was 1 to 20 and by C. speciosus was 1 to 5. Anisakis sp. and these two species of Trypanothyncha were reported in A. monoceros for the first time.