[Problem] To provide a polypeptide which has highly homogeneous sialylated sugar chains attached thereto and has an interferon β activity.[Solution] A sugar chain-containing polypeptide that is selected from the group consisting of (1) to (4):(1) a polypeptide which comprises the amino acid sequence represented by SEQ ID NO:1；(2) a polypeptide which comprises an amino acid sequence derived from the amino acid sequence represented by SEQ ID NO:1 by deletion, substitution or addition of one to several amino acids；(3) a polypeptide that is an analog of interferon β； and(4) a polypeptide that has an 80% or higher homology with the polypeptide comprising the amino acid sequence represented by SEQ ID NO:1,wherein amino acids at 4-6 positions are substituted with amino acids having sugar chains attached thereto, and all of non-reducing ends of these sugar chains are sialylated.
