Introduction A new coccidian species of the genus Eimeria Schneider, 1875 (Apicomplexa: Eimeriidae), is reported from the bat host Myotis riparius Handley from Ilha Grande, a large island of the coast of the State of Rio de Janeiro, in southeastern Brazil. Methods: Bats were captured in 13 mist nets (10×3 m), which were set within the experimental plots, and through active searches of the daytime roosts of Molossus molossus Pallas found in Vila Dois Rios. Containment was made in bags for the collection of feces and identifcation of coccidia. A survey was conducted on the coccidia species described so far (Table 2). Results: The oöcysts of Eimeria riparii n. sp. are ellipsoidal to cylindroidal with an extremely thin, bi-layered wall, slightly rough. Two polar granules are present, micropyle and oöcyst residuum are both absent. The sporocysts are ellipsoidal, the sporocyst residuum is formed by sparse, rounded granules of varying sizes; the Stieda body is trapezoidal and a sub-Stieda body is absent. Sporozoites are banana shaped. With the new species described here, a total of 40 Eimeria spp. have been described infecting bat hosts, belonging to 30 species of 18 genera and 5 families. Conclusion: The subsequent increase in the known diversity of bats has been derived from the ongoing expansion of research in a number of diferent areas of taxonomy and ecology although the number of studies of the associated coccidian parasites of the family Eimeriidae has increased more slowly.