Abstract: As a new type of immunoglobulin, IgT (Immunoglobulin T) plays an important role in mucosal immunity. The prokaryotic expression vector of Nile tilapia IgT was constructed according to its gene sequence to obtain the IgT recombinant protein, weighing 75103 Da approximately, and the mouse polyclonal antibody against IgT with high titer was prepared. Expression analysis showed that IgT was expressed in various tissues, and the relatively high expression was in spleen, skin, intestine and gills. The relative expression of IgT mRNA in the head kidney and skin was significantly up-regulated in 12 h and 4 d after the infection of S.agalactiae. The results of immunohistochemistry revealed that IgT protein had a small amount of distribution in the head kidney and skin; however, there was an obvious up-regulation in the skin after the stimulation of S.agalactiae. Taken together, the results of this study indicate that IgT plays a main role in mucosal immunity of Nile tilapia.