Triazolyl-DNA (TLDNA), DNA wherein phosphodiester units are replaced by triazole units, is of great interest. By adopting Topochemical Azide–Alkyne Cycloaddition (TAAC) reaction, we have synthesized homobasic TLDNA oligomers. 5′-ethynyl-3′-azido-2′,3′,5′-tri-deoxycytosine, which crystallized with proximal placement of azide and alkyne units of adjacent molecules, underwent TAAC reaction to TLDNA oligomers.