Toxoplasma gondii infects several species of marine mammals, including wild and captive ones, in countries of America, Europe, and Asia. The infection of these animals, which act as sentinels for the presence of T. gondii and other agents, indicates contamination of the marine environment by oocysts. This study aims to report the isolation of Toxoplasma gondii in a "Porpoise" (Pontoporia blainvillei) collected after death in the municipality of Laguna, South Coast of State of Santa Catarina, Brazil. A necropsy was performed on a juvenile, sex undetermined (possibly due to the action of scavenger birds), by the Santos Basin Beach Monitoring Project (section 1). Heart, lung, brain, and liver samples were processed in a pool for enzymatic digestion and use in the bioassay in mice. The digestion product was subcutaneously inoculated into three mice (1 mL each), which were observed daily for the evaluation of clinical signs compatible with T. gondii infection and then euthanized. Serum, organs (brain, heart, and lung), and peritoneal lavage were collected from euthanized mice to detect antibodies (Indirect Immunofluorescence Reaction – IFAT; cut-off 1:16), cysts and tachyzoites, respectively. Brain fragments were analyzed (squash) for the search for cysts and lung imprint and peritoneal lavage searching for tachyzoites. The three mice died at 21 days after inoculation and presented tachyzoites in the peritoneal lavage and lung imprint. Two of the three mice had antibodies against T. gondii with titers of 1:64 and 1:256. To the authors' knowledge, this is the first report of isolation of T. gondii in P. blainvillei. T.he diet of Pontoporia blainvillei is based on eating fish such as anchovies and sardines, which have the characteristic of bioaccumulating molecules, among them, oocysts. In addition, these species of fish are also used in human food. This fact highlights the importance of determining T. gondii infection in marine mammals, which can act as indicators for the risk of infection in humans.