AbstractHymenolepis nana, typically a parasite found in conventionally established mouse colonies, has zoonotic potential characterized by autoinfection and direct life cycle. The objective of this study was to determine the rate of parasite infection in laboratory mice. The hymenolepidide cestode infected 40% of the 50 mice sampled. The rate of infection in males (52%) was higher than in females (28%). Morphological studies on the cestode parasite showed that worms had a globular scolex with four suckers, a retractable rostellum with 20–30 hooks, and a short unsegmented neck. In addition, the remaining strobila consisted of immature, mature, and gravid proglottids, irregularly alternating genital pores, lobulated ovaries, postovarian vitelline glands, and uteri with up to 200 eggs in their gravid proglottids. The parasite taxonomy was confirmed by using molecular characterization based on the sequence analysis of the mitochondrial cytochromecoxidase subunit 1 (mtCOX1) gene. The parasite recovered was up to 80% identical to other species in GenBank. High blast scores and low divergence were noted between the isolated parasite and previously describedH. nana(gb| AP017666.1). The phylogenetic analysis using theCOX1sequence places this hymenolepidid species of the order Cyclophyllidea.