Synthesis of self-activated peptide nucleic acid (PNA) monomers and an efficient method for PNA synthesis using a benzothiazole-2-sulfonyl (Bts) group as an amine-protecting group as well as an acid-activating group are reported. Couplings were complete within 120 min, and the deprotection was performed in 10 min. This Bts strategy provides a high purity PNA oligomer and is appropriate for large-scale synthesis. The results of the 15-mer PNA oligomer are described.