Abstract: The gene fragment EC of 2744-2947nt of antigenic domain A of CSFV was cloned and expressed using BactoBac baculovirus expression system. The antigenicity of EC expression product was analysed. The results showed that the expression product can bind to the neutralizing MAbs c2410 and a18 with specificity, and it can also elicit neutralizing antibodies in immunizing animals. The results indicated that antigenic subdomain A1 is located between amino acid 791 and 858 of E2 protein.