The object of the present invention is to provide a glycosylated polypeptide having uniform sugar chain structure which has interferon β activity. It was found that a glycosylated polypeptide having uniform sugar chain structure as well as having interferon β activity can be prepared by a method comprising a step of synthesizing a glycosylated peptide fragment and at least two peptide fragments and a step of linking the glycosylated peptide fragment and the at least two peptide fragments.