Abstract: A method of delivering antigenic peptide into the endoplasmic reticulum by the fusion protein includes: (a) preparing a fusion protein with a Tat-derived peptide, a (His)6 peptide, a ubiquitin, and an antigenic peptide provided in turn from the N-terminal end to the C-terminal end; (b) delivering the fusion protein across the cell membrane into the cytosol through the Tat-derived peptide; (c) cleaving the antigenic peptide from the fusion protein by cytosolic ubiquitin C-terminal hydrolases; and (d) transporting the antigenic peptide into the endoplasmic reticulum (ER) by a TAP1/2 transporter on the ER membrane.