The present invention relates to: a fusion polypeptide in which an anti-inflammatory polypeptide and a ferritin monomer fragment are bound; and a pharmaceutical composition for treating inflammatory diseases, containing the same as an active ingredient and, more specifically, to: a fusion polypeptide in which an anti-inflammatory polypeptide is fused to an N-terminus and/or a C-terminus of a ferritin monomer fragment from which a portion of a fourth loop and a fifth helix, of a human derived ferritin monomer, are removed; and a use thereof for treating inflammatory diseases. As in the above, the fusion polypeptide, which has an amino acid sequence represented by SEQ ID NO: 1 and in which an anti-inflammatory polypeptide is fused to an N-terminus and/or a C-terminus of a fragment of a human-derived ferritin monomer, can fuse two types of anti-inflammatory polypeptides, acting through different mechanisms, into a nano cage and administer the same, and thus the fusion polypeptide can exhibit an excellent effect in the treatment of inflammatory diseases including sepsis.