To provide a method for printing ink to a heat-sensitive tacky sheet, capable of efficiently printing without blocking the heat-sensitive tacky sheet and impairing beauty of printing both surfaces.

In printing ink onto other surface of a heat-sensitive tacky sheet in which a heat-sensitive tackifier layer which is non-adhesive at normal temperature, but develops tackiness by heating is provided on one side of a substrate, a printing index PI value defined in the formula is ≥5.0, preferably 10.0-40.0. Furthermore, in the formula, TA: a temperature[°C] at which a heat- sensitive tackifier starts to develop tackiness; TO: a temperature[°C] on coated surface of a tackifier of a heat-sensitive tacky sheet before printing; T: a maximum temperature[°C] on printed surface in ink drying step; α: heat diffusion ratio [mm2/s] in thickness direction of a heat-sensitive tacky sheet; (t): required time [s] of ink drying step; Z: thickness [mm] of a heat-sensitive tacky sheet. UV-curable ink is preferably used as the printing system and ink is preferably dried by UV irradiation.