The object of the present invention is to provide a polypeptide having interferon β activity glycosylated with highly uniform sialylated sugar chains. The present invention is a glycosylated polypeptide, wherein the polypeptide is any polypeptide selected from the group consisting of the following (1) to (4)； (1) a polypeptide consisting of the amino acid sequence represented by SEQ ID NO. 1, (2) a polypeptide having one or a few amino acids deleted, substituted, or added in the polypeptide consisting of the amino acid sequence represented by SEQ ID NO. 1, (3) a polypeptide that is an analog of interferon β, and (4) a polypeptide having 80% or more homology to the polypeptide consisting of the amino acid sequence represented by SEQ ID NO. 1, in which amino acids at 4 to 6 locations are substituted with glycosylated amino acids, and wherein all of the non-reducing terminals of said sugar chain are sialylated.
