Carcasses of whales provide much valuable information on their natural history. However, some specimens cannot be identified in the field due to the advanced state of decomposition. In this study, the DNA was extracted and the mitochondrial cytochrome b gene was amplified by polymerase chain reaction and sequenced for four carcasses of possible mysticeti (GEMM: 075, 088, 135 and GEMARS: 1302). A blast search using the nucleotide–nucleotide basic local alignment (blastn) search tool was conducted using the generated sequences. Samples GEMM 075 and GEMARS 1302 showed 98% identity to one sequence of Balaenoptera acutorostrata. Samples GEMM 088 and GEMM 135 showed 99% identity to sequences from Balaenoptera edeni and Megaptera novaeangliae, respectively. A neighbour-joining tree was generated using sequences from GenBank from all species of balaenopterid that occur on the coast of Brazil. The results showed that all carcasses analysed were correspondent to species from the family Balaenopteridae already recorded in Brazil.