Abstract: It is intended to provide a positively charged liposome, particularly having a polyarginine peptide on a surface thereof, which is capable of increasing the resistance to a negatively charged biological component such as a protein in the blood and maintaining a high ability to deliver a substance even in the blood. An agent for enhancing the resistance of liposome against biological component comprising a peptide having at least one of the following characteristics (a) and (b) as an active ingredient: (a) A peptide comprising an amino acid sequence represented by SEQ ID No: 1 or 2; and (b) A peptide comprising an amino acid sequence represented by SEQ ID No: 1 or 2, in which one or more amino acids are deleted, substituted or added, and having an activity for promoting lipid membrane fusion under acidic condition.