In recent years, streptococcal diseases have severely threatened the development of tilapia aquaculture, but effective prevention and control methods have not yet been established. To understand the immune responses of vaccinated Nile tilapia, digital gene expression (DGE) technology was applied in this study to detect the gene expression profile of the Nile tilapia (Oreochromis niloticus) liver in response to ScpB vaccination and a Streptococcus agalactiae-challenge. The control and the ScpB-vaccinated Nile tilapia yielded a total of 25,788,734 and 27,088,598 clean reads, respectively. A total of 505 differentially expressed unigenes were detected, of which 236 were significantly up-regulated, and 269 were significantly down-regulated.