Abstract: Streptococcus suis serotype 2 (SS2) is a zoonotic infectious pathogen associated with a wide range of diseases in human health and pig industry This article aims to study the role of SsnA gene as a molecular diagnosis marker in the differential diagnosis of SS2-SsnA gene was amplified using SS2-LT genome DNA as template and the sequence was then inserted into expression vector pET-28a(+). The plasmid was introduced into E- coli BL21(DE3) for expression and 46 kD recombinant protein was obtained, which had been proved to be immunoreactive by SDS-PAGE and Western blotting. An SsnA-ELISA diagnostic method was developed by using the purified SsnA fusion protein as coating antigen. The detected results of immune serum and infected serum were compared by using SsnA-ELISA Kit, and the significant difference （P<0.05） presented indicates that the established SsnA-ELISA owns excellent detecting effect. 1 446 serum samples collected from 8 provinces of China were then tested by SsnAELISA Kit and the result show that the positive rate ranged from 0%-14.77% and the average positive rate was 5.39%. Our study show that SsnA of Streptococcus suis serotype 2 could be used as a good molecular diagnosis marker in distinguishing infected or immunized animals; in addition, our clinical data indicates that there exists an evident relationship between the infection and epidemicity of SS2 and its climatic environment.