The tropical dry forests of Mexico are one of the world’s biodiversity hotspots. To contribute to the knowledge of mammal diversity and conservation of the central coast of Oaxaca State, southern Mexico, we conducted field surveys in the area. Additional information was obtained from literature and museum databases. In order to compare the taxonomic similitude between areas along the Planicie Costera del Pacífico province we performed a taxonomic similarity analysis using data from the literature and the present study. A total of 49 species of mammals belonging to 19 families and eight orders were recorded. The maximum number of species was recorded in deciduous forest (n = 46), followed by semideciduous forest (n = 11). The similarity index was low (<50%) between areas along the Planicie costera del Pacífico, indicating higher species turnover. The high mammal diversity, the presence of endemic (8%), threatened species (16%), and voluntary conservation areas highlight the importance of this region.