Abstract: The present invention relates to: a recombinant peptide in which a Mitochondria Localization Sequence (MLS) peptide and the Signal Transducer and Activator of Transcription 3 (STAT3) are fused to each other; a recombinant vector carrying a polynucleotide coding for the recombinant peptide; and a composition comprising the recombinant peptide or the recombinant vector as an active ingredient for prevention or treatment of autoimmune disease or inflammatory disease, wherein the recombinant peptide or the recombinant vector allows STAT3 to be overexpressed in the mitochondria to enhance the mitochondrial function, resulting in inhibiting the expression of inflammatory cytokines including IL-17, whereby the composition may be advantageously used for preventing or treating autoimmune disease or inflammatory diseases.