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<p>Abstract</p> <p>Background</p> <p>Small heat shock proteins are ubiquitous family of stress proteins, having a role in virulence and survival of the pathogen. <it>M. leprae</it>, the causative agent of leprosy is an uncultivable organism in defined media, hence the biology and function of proteins were examined by cloning <it>M. leprae </it>genes in heterologous hosts. The study on sHsp18 was carried out as the knowledge about the functions of this major immunodominant antigen of <it>M. leprae </it>is scanty.</p> <p>Results</p> <p>The gene encoding <it>Mycobacterium leprae </it>small heat shock protein (sHsp18) was amplified from biopsy material of leprosy patients, and cloned and expressed in <it>E. coli</it>. The localization and <it>in vitro </it>characterization of the protein are detailed in this report. Data show that major portion of the protein is localized in the outer membrane of <it>E. coli</it>. The purified sHsp18 functions as an efficient chaperone as shown by their ability to prevent thermal inactivation of restriction enzymes <it>Sma</it>I and <it>Nde</it>I. Physical interaction of the chaperone with target protein is also demonstrated. Size exclusion chromatography of purified protein shows that the protein can form multimeric complexes under <it>in vitro </it>conditions as is demonstrated for several small heat shock proteins.</p> <p>Conclusion</p> <p>The small heat shock protein sHsp18 of <it>M. leprae </it>is a chaperone and shows several properties associated with other small heat shock proteins. Membrane association and <it>in vitro </it>chaperone function of sHsp18 shows that the protein may play a role in the virulence and survival of <it>M. leprae </it>in infected host.</p>