Twelve dinucleotide polymorphic microsatellite loci were isolated from the marine tucuxi dolphin (Sotalia guianensis). Levels of genetic diversity were assessed using 34 individuals from the coasts of Rio de Janeiro and Pará, Brazil. Numbers of alleles varied between two and 14, and observed and expected heterozygosities ranged from 0.040 to 0.704, and from 0.093 to 0.818, respectively. Moreover, eight of these loci were variable in the riverine tucuxi Sotalia fluviatilis. This is the first description of microsatellite primers from a dolphin that does not belong to the Delphininae. These loci are currently being used in the analysis of population structure of both tucuxi species.