Leporinus elongatus is an important commercial fish found in the La Plata and Paraná River basins. Next-generation sequencing was used to sequence the mitochondrial DNA (mtDNA) of L. elongatus. The mtDNA was assembled using the CLC Workbench software v. 9.0 and subsequently aligned to other 10 complete fish mitochondrial sequences to enable phylogenetic analysis using MEGA 7.0. The complete mtDNA molecule had 16,784 bp and its GC content was 43%. The mtDNA structure was similar to that of other vertebrates: two ribosomal RNA, 22 transfer RNA, 13 protein-coding genes, and a D-loop region containing 1115 bp. Phylogenetic analysis yielded a tree with high bootstrap value that was coherent with the current phylogeny proposed for Characiformes.