Abstract: We have amplified, cloned and determined the sequence of Streptococcus agalactiae luxS gene from Tilapia sp. by PCR. The characteristics of the deduced luxS protein were predicted by ExPAsy software; the 3D structures of luxS and the deduced protein were established and analyzed by SWISS-Model and SwisS-PDBviewer software, respectively. The results indicate that the deduced luxS protein contains conserved active center and Zn²⁺ binding site, which may affect biofilm formation and regulate virulence factor. The Ramachandram plot shows that the structure of modeled luxS protein is reasonable.