A method for transparentizing biological tissue in a living state, which comprises applying a solution to the biological tissue, the solution containing one or more compounds selected from the group consisting of a nucleotide, a nucleotide derivative, a macromolecule containing a nucleotide or a nucleotide derivative, and a nucleotide polymer; a composition for transparentizing biological tissue in a living state, which comprises the aforementioned compound; and a kit for transparentizing biological tissue in a living state, which comprises the aforementioned compound.