Mnemiopsis leidyi is probably the most globally studied ctenophore species due to its abundance in American estuaries, and because the species is one of the most successful marine bioinvaders in the Mediterranean, Caspian, and Black Seas, among others places. The species’ high capacity to tolerate low levels of dissolved oxygen, variations in salinity, as well as extremely low and high temperatures all aid in the success of the species. In the Colombian Caribbean, no formal records of Ctenophora or reference material to support the presence of M. leidyi exist. The objectives of this work were to taxonomically identify the ctenophoran species that inhabits Mallorquín Lagoon (located in the central area of the Colombian Caribbean coast) and to establish relationships between species presence and physical–chemical parameters (temperature, dissolved oxygen, pH, salinity). Specimens were collected during six sampling events from September 2018 to January 2019 from six stations in the coastal lagoon (n=35 total sampling events). Mnemiopsis leidyi was identified based on morphological characteristics. Mnemiopsis leidyi individuals were collected at five of six stations. As well, M. leidyi was not observed in some sampling events, possibly due to an increase in the freshwater flow to the coastal lagoon by the León Creek tributary. M. leidyi was found mainly in hypoxic locations, with values between 1.68 - 5.05 mg/L. This work is the first confirmed record of M. leidyi in the Colombian Caribbean and provides ecological knowledge of the species in brackish coastal Mallorquín Lagoon. These results are an important basis for the continued monitoring of the species relative to the changing conditions of Mallorquín Lagoon.