Among the known interferon-induced antiviral mechanisms, the Mx pathway is one of the most powerful pathways. The Mx protein has direct antiviral activity and inhibits a wide range of viruses by blocking an early stage of the viral replication cycle. Cloning, characterization, and expression of Mx in vivo and in vitro have been conducted. The chicken Mx gene spans 21 kb and is made up of 14 exons and 13 introns, of which the promoter region was analyzed. The real-time PCR results showed that Mx expression was increased in chicken embryo fibroblasts (CEF) after 12- and 24-h induction with polyI: C. Induction of Mx expression by poly I: C in vivo revealed tissue-specific patterns among the chicken tissues tested. A trace expression of Mx was detected in healthy chicken liver tissues from adult chickens without inducement; the expression levels in the liver, heart, and gizzard were higher than in the muscle and kidney. This is the first report to demonstrate the expression of a glutathione-S-transferase-tagged-Mx fusion protein of 75 KDa, as well as the biological activity tested by SDS-PAGE and western blotting.