a reusable thermal ink sheet used for thermal printing has a thermal ink composition layer formed on a substrate . the thermal ink composition is a mixture of ink material and filler . the ink material includes a coloring agent and a low temperature melting compound which is a solid at room temperature and is melted during thermal printing in response to a printing image to be transferred . the low temperature melting compound contains a urethane compound as a base material and additive materials as viscosity modulators thereof which lower the viscosity of the ink material at printing temperature . the additive materials contain at least one material selected from the group consisting of fatty acid compounds , fatty acid amide compounds and ester compounds . the improved ink sheet assures a high quality printing image is transferred to a plain paper having a rough surface when thermal printing occurs ten times or more . in addition , ghost images are not formed and background noise is eliminated . further , a plasticizer is added to the ink material described above , thereby improving the thermal printing ability at a low temperature .