As an obligate intracellular pathogen, the principal host cells for Mycobacterium leprae are mononuclear phagocytes or macrophages. The macrophage is a primitive cell type being found in both early and advanced life forms, and possesses a variety of functions, such as phagocytosis of invaded bacteria, production of cytokines, antigen presentation and tumor killing. Hansen's disease is a chronic infectious disease characterized by specific host immune responses against M. leprae. In this article the macrophage is focused to dissect its functions in the disease.