Morphometric characteristics of blood cells were examined in 44 (16 males, 28 females) Bolson tortoises (Gopherus flavomarginatus) in Mapimí, Mexico. Blood samples were drawn from the subcarapacial vein, and smear stains were used to differentiate and measure the diameter and surface area of cells. Mature and polychromatophilic erythrocytes were identified, as well as five types of leukocytes (lymphocytes, heterophils, eosinophils, basophils and monocytes), and thrombocytes. The shape and color of G. flavomarginatus blood cells were similar to those reported for the G. agassizii, and G. polyphemus species. Blood cell sizes fitted related data from other reptile species. The information generated in this study can help monitor the health status of G. flavomarginatus individuals in the wild, thus advancing efforts to protect this endangered species.