Although information on the fauna of helminths of the shortfin molly Poecilia mexicana in freshwater environments is extensive, to date, there have been no studies on helminths that parasitize this fish in brackish water bodies. To increase the knowledge about the host-parasite association in this kind of habitats, during April 2014, 80 fish specimens of P. mexicana from 2 localities in Veracruz, Mexico, were examined for helminths: Arroyo Moreno (AM) and Laguna Mandinga (LM). Arroyo Moreno is an anthropogenically polluted mangrove swamp, and LM is a saline environment with low marine influence. The helminth species record in both fish populations included 9 taxa: 7 digeneans, 1 cestode, and 1 nematode, with 6,261 individuals, most of them collected in fishes from AM (5,768). In general, a high proportion of allogenic larval stages was observed, which agreed with the pattern observed in helminth fauna of tropic freshwater fish. In addition, these parasite assemblages were dominated by digeneans, worms that generally are numerically dominant in many helminth communities of freshwater fishes in Mexico. The euryhaline nature of P. mexicana establishes it as an adequate system to study the effects of salinity gradients focused on helminth communities.