In the present study, mammary tissues from the fruit bat (Carollia perspicillata) and mouse (Mus musculus) were compared using histological and immunohistochemical methods. Because the female bat exhibits greater reproductive similarities to humans, it might provide a useful animal model for studying mammary physiology and disease with relevance to our own species. In lactating and recently lactating specimens, bat tissue had significantly fewer adipocytes and more collagenous connective tissue compared to the mouse. The proteins Stat5a, keratin 5, Npt2b, and E-cadherin were all similarly localized in mouse and bat mammary tissues taken from lactating animals. The present study demonstrates that whereas the epithelial compartment and the presence of differentiation markers are conserved between the mouse and bat, differences exist in the stromal compartment.