A synthetic plasmid in which DNA encoding protein of a feline interferon is integrated, a transformant obtainable by the transformation of a host cell by the use of the syn­thetic plasmid and a feline interferon having a biological activity given by a protein carrying a specific amino acid sequence, a feline interferon gene encoding the feline in­terferon, a feline interferon precursor comprised of a cleavable peptide or a signal peptide being linked to the N terminal of the feline interferon, a feline interferon pre­cursor gene encoding the feline interferon precursor and a method for producing the feline interferon, which are ap­plied to the mass production of a feline interferon to be used as a remedy for feline viral disease and tumor.