is a causative agent of mucous-sloughing disease and bacterial enteritis in fish, with high morbidity and mortality. Toxin-coregulated pilus (TCP) is a major virulence factor of As a major structural protein of TCP, toxin-coregulated pilin A (TcpA) is potential candidate for vaccine development. In this study, the diseased grass carp (gene fragment containing the open reading frame (ORF) was then subcloned into pGEX-4T-1 to construct expression plasmid pGEX-4T-1-tcpA. The recombinant fusion protein (rGST-TcpA) was expressed by IPTG induction incharacterization. Sequence analysis revealed that the ORF of thegene from the Y1 strain (GenBank accession no. EU649677) is 657 bp and encodes a protein of 224 amino acids. The gene is 99.6%–9% identical at the protein level to seven tcpA sequences in GenBank, which suggested that the TcpA protein is considerably conserved. SDS-PAGE analysis showed that the 47.0 kD rGST-TcpA fusion protein was mainly expressed in inclusion bodies. Western blotting demonstrated that rGST-TcpA could react specifically with mouse antisera raised against the pilus protein of strain Y1. The purified rGST-TcpA was used to immunize ). The titer of the antisera was 1:16, as determined by a double immunodiffusion test, and it could significantly inhibit adherence of Y1 strain to HEp-2 cells . A relative percentage survival (RPS) of 73.33% was found in immunized challenge at day 25 after immunization. This study indicated that the rTcpA protein possess the same immunogenicity, immunoreactivity, and