麻风杆菌也称为韩森氏杆菌，是一种可引起麻风病的分支杆菌，菌体呈短小棒状或稍弯曲，长约2-6µm，宽约0.2-0.6µm，抗酸染色呈红色（抗酸性），革兰氏染色呈阳性，好氧菌。

于1873年由挪威医生格哈德·阿玛尔·汉生在麻风病人的皮肤结节中发现。

Mycobacterium leprae, also known as Hansen’s bacillus spirilly, mostly found in warm tropical countries, is a Gram-positive bacterium that causes leprosy (Hansen's disease). It is an intracellular, pleomorphic, acid-fast, pathogenic bacterium. M. leprae is an aerobic bacillus (rod-shaped) surrounded by the characteristic waxy coating unique to mycobacteria. In size and shape, it closely resembles Mycobacterium tuberculosis. Due to its thick waxy coating, M. leprae stains with a carbol fuchsin rather, than with the traditional Gram stain. The culture takes several weeks to mature.