Mx protein is one of the classes of antiviral proteins induced by type I interferon (IFN).A full length cDNA sequence of Mx gene from grass carp (Ctenopharyngodon indellus) was amplified using reverse transcription polymerase chain reaction (RT PCR) with total RNA extracted from Ctenopharyngodon indellus kidney (CIK) cells treated with PolyI∶C and cloned into pMD20-T vector named pMD20-T-Mx, and sequenced. The recombinant plasmid pMD20-T-Mx and eukaryotic expression vector pEGFP-C1 were cleaved by restriction endonuclease, Mx gene full-length cDNA sequence linkaged with pEGFP-C1. The data indicate that grass carp Mx gene full length cDNA sequence has 1 921 nucleotides, encoding 627 amino acid residues of the mature peptide with a molecular weight of about 71.1 ku and a theoretical isoelectric point of 8.33. The grass carp Mx protein contains a triparitite guanosine 5′-Triphosphate(GTP) binding motif and a dynamin family signature sequence, which are conserved in all IFN induced Mx proteins of the vertebrates. Bioinformatics analysis reveals that the protein encoded by Mx gene in grass carp is hydrophilic in most regions and has rich B cell antigenicity positions without obvious nuclear localization signal sequence. The dimensional structure of the grass carp Mx protein includes GTPase domain in the amino terminus region, central interactive domain (CID) in the middle and GTPase effector domain (GED) in the carboxyl terminus region. Comparative analysis shows that the Mx protein amino acid sequence of grass carp shares similarity of 45.1%-99.7% to those of other species. pEGFP-C1-Mx, which contains 〗Mx gene full length cDNA sequence and EGFP gene, has been constructed.