Abstract: Tilapia is one of the most important aquaculture fish in China. In recent years，the tilapia aquaculture industry was seriously damaged by the frequently outbreak of streptococcicosis. In this review，the transmission routes of Streptococcus agalactiae，intestinal colonization and the mechanisms of immune evasion were discussed aim to provide useful idea for further research on pathogenesis of S. agalactiae and the prophylaxis and therapy for streptococcicosis of tilapia.