To provide a peptide which can be produced and processed more readily compared with prothymosin α, which is conventionally known, or a peptide thereof and has an activity at a level equivalent to or higher than that of prothymosin α or a peptide thereof. The present invention provides an ameliorating agent for blood-organ barrier dysfunction, a therapeutic agent for diseases associated with blood-organ barrier dysfunction or ischemic diseases or a nerve cell death inhibitor, each comprising, as an active ingredient, a peptide comprising the amino acid sequence represented by SEQ ID NO: 1 or a peptide having substantially the same function as that of the aforementioned peptide.
