A reagent for imaging an advancing intracellular acetylation, for example, an acetylation that is advanced by the action of acetyl-CoA in the mitochondria, at high sensitivity and high efficiency, which comprises a combination of a rhodamine derivative that is substantially non-fluorescent before being acetylated, and emits strong fluorescence after being acetylated, and an acylation catalyst and/or an acylation reaction-promoting agent.
