Background and Aims: The genus Mycoporum of the class Dothideomycetes of the phylum Ascomycota is characterised by ascostromata with scattered, aggregated locules without a wall of their own, bitunicate asci with a short pedicel, as well as ellipsoidal, fusiform to clavate ascospores with broader upper hemispores, and a variable number of septa. The objective of this study is to report Mycoporum buckii for the first time in Mexico. Methods: The specimens were collected on Rhizophora mangle bark in the Cozumel Island Biosphere Reserve, Quintana Roo, Mexico, in 2019, and were deposited in the herbarium ENCB of the Instituto Politécnico Nacional, Mexico. The material was reviewed in dry state, and macro- and micro-morphological characters were described. Specimens were identified with specialised keys and literature. Key results: The description of Mycoporum buckii of Mexico is presented. This species is characterised by multilocular, sessile ascostromata, clavate asci, and ellipsoidal ascospores with one transversal septum. Conclusions: Mycoporum buckii grows on Rhizophora mangle and produces its sporomas during the rainy and dry seasons in the Cozumel Island Biosphere Reserve, Quintana Roo, Mexico.