The RD-1 locus has been considered crucial in the pathogenesis of M. tuberculosis, the RD-1 locus is 9.5 kb and spanning open reading frames Rv3871 to Rv3879c encoding 9 different proteins separately. The RD-1 locus is missing in all bacillus Calmette-Guerin (BCG) strains, and is one of the key virulence factor in M. tuberculosis. The RD-1 locus participates in a new secreting system named ESX-1, which can facilitate the secretion of some special proteins. The two important proteins encoded by the RD-1 locus named CFP-10 and ESAT-6 can form a tight 1∶1 complex, and has been shown to be coordinately secreted and lead to a strong T cell response, which suggests that these two proteins may act as ideal target antigens in diagnosis and prevention of tuberculosis (TB).