Mx proteins are main effectors of the antiviral innate immune response mediated by type I interferon (IFN I). Actually, diverse Mx proteins from fish proved highly active against fish viruses, standing out among them the Mx1, Mx2 and Mx3 from gilthead seabream (Sparus aurata), a species exhibiting a natural resistance to viral diseases. In this study, the structure and functional activity of their corresponding promoters (pMx1, pMx2 and pMx3) have been assessed. The three promoters present an identical 3′ region of 157 bp, exhibiting a single canonical interferon-stimulated response element (ISRE), which is indispensible for the poli:IC induction of pMx1 and pMx3, while not for that of pMx2. In the remaining part of the three promoters other regulatory motifs were identified, as gamma IFN activated sites in variable number (1, 4 and 2 in pMx1, pMx2 and pMx3, respectively), as well as several independent GAAA elements or ISRE core sequences (13, 15 and 12 in pMx1, pMx2 and pMx3, respectively). The structural dissimilarities shown by the three promoters parallels with the differences observed in their response profiles, in terms of the time course of the induction, and basal and induced expression levels of each promoter. Altogether, these findings indicate that the expression of Mx1, Mx2 and Mx3 genes from the gilthead seabream might be specifically regulated, in accordance with the functional role of each Mx protein in the successful antiviral response shown by this species.