Abstract: The present invention relates to a nucleic acid complex having a novel structure, which can introduce a bioactive nucleic acid into cells, a composition for treating and diagnosing disease, which comprises the same, and a method of regulating expression of a target gene using the same, and more particularly to a nucleic acid complex comprising a bioactive nucleic acid complementarily bound to a carrier peptide nucleic acid modified to be generally positively charged, a composition for treating and diagnosing disease, which comprises the same, and a method of regulating expression of a target gene using the same.