A method for conjugating a nucleic acid with a molecule is provided. The method includes steps of (a) reacting the nucleic acid having a 5′-monophosphate with an activating agent in a first buffer to form a solution (b) mixing an alcohol with the solution formed in the step (a) to obtain an intermediate and (c) dissolving the intermediate in a second buffer containing an ethylenediaminetetraacetic acid (EDTA) and adding a nucleophile thereinto to react the intermediate with the nucleophile.
