A new coccidian parasite of the genus Caryospora is described from a long nosed vine snake, Ahaetulla nasuta, Lacépède, 1789 from Thailand. Oocysts of Caryospora ahaetullae sp. n. are spherical or slightly subspherical, 24.8 (22.5-26.0) pm in diameter, with a single-layered wall about 0.75 pm thick. A micropyle or oocyst residuum is absent. One, rarely two, polar granules are present, 1.5-2.0 pm. Sporocysts are ellipsoidal, 18.5 x 14.2 (18.0-19.5 x 13.0-15.0) pm with prominent Stieda and substieda bodies. Sporocyst residuum present, consisting of numerous very small granules scattered among 8 sporozoites. Sporo-zoites, with prominent transverse striations anteriorly, are vermiform, 15.0 x 3.8 (13.5-16.5 x 3.5—4.5) pm (in situ), lying lengthwise and parallel within sporocyst. Each sporozoite contains a spherical anterior and spherical to subspherical posterior refractile bodies.