PURPOSE: To enhance heat resistance and running properties by providing a back coat material film to the rear of a base film and forming the back coat material from a mixture of an acrylic/silicone graft polymer and a reaction product of amino modified silicone oil and polyfunctional isocyanate.

CONSTITUTION: A thermal transfer ink sheet is formed by providing a thermal transfer ink layer to a base film and providing a back coat material film to the rear of the base film. The back coat material is constituted of a mixture of an acrylic/silicone graft polymer and a reaction product of amino modified silicone oil and polyfunctional isocyanate. The acrylic/silicone graft polymer is a resin obtained by the graft polymerization of a (meth)acrylic ester monomer and (meth)acrylic acid modified silicone oil and the (meth)acrylic ester part has the adhesiveness with the base film and heat resistance and the (meth)acrylic acid modified part has lubricity.