Melanoma differentiation-associated gene 5 (MDA5) is an important cytoplasmic RNA sensor that detects viral double-stranded RNA in innate immunity. The objective of this study was to characterize the structure and function of the MDA5 gene in the duck. In this study, full-length duck MDA5 (duMDA5) complementary DNA (cDNA) was obtained using the reverse transcription-polymerase chain reaction and rapid amplification of the cDNA ends. The cDNA consisted of a 123 nucleotide 5′ untranslated region (UTR), a 735 nucleotide 3′ UTR, and a 3012 nucleotide open-reading frame, encoding 1003 amino acids. Multiple sequence alignments showed that duMDA5 had 91.18% and 83.11% amino acid sequence similarity with geese and chicken MDA5, respectively, as well as 59.76%–61.26% sequence identity with mammalian homologs. Phylogenetic analysis demonstrated that MDA5 has been highly conserved throughout vertebrate evolution. Quantitative real-time polymerase chain reaction analysis indicated that the duMDA5 mRNA is scarcely detected in healthy tissues and the highest relative transcript level of duMDA5 was induced during poly(I:C) stimulation. Furthermore, knockdown duMDA5 significantly inhibited the transcription of poly(I:C)-induced beta interferons, nuclear factor kappa-B, interferon regulatory factor 7, translocated intimin receptor domain-containing adaptor protein inducing beta interferons, interferon-induced GTP-binding protein, signal transducer and activator of transcription 1 and 2 mRNA. Taken together, these results suggest that duMDA5 is an important receptor for inducing antiviral activity in the duck’s innate immune response.