The present invention relates to an amino acid-modified human interferon alpha isoform having at least one of the Asn-Xaa-Ser/Thr (N-X-S/T) sequence formed at a specific site so that glycosylation takes place at this site and a gene encoding the same, an expression vector comprising the gene, and a method for producing glycosylated human interferon alpha isoform by transforming or transfecting an eukaryotic cell with the expression vector, culturing the transfected or transformed cell and isolating the glycosylated human interferon alpha isoform from the culture, the glycosylated human interferon alpha isoform produced therefrom and a pharmaceutical composition comprising the same.