PURPOSE: To enhance heat sensitivity and enhance heat resistance and anti- sticking property, by adding a specified copolymer to a color forming layer.

CONSTITUTION: A copolymer of acrylic acid and/or methacrylic acid with an unsaturated dicarboxylic acid or a salt of the copolymer is incorporated into the color forming layer. By this, adhesion of scum to a head is prevented from occurring, and a thermal recording paper excellent in high-speed printing characteristics is obtained. The copolymer preferably comprises 95W30mol% of acrylic acid and/or methacrylic acid and 5W70mol% of the unsaturated dicarboxylic acid, and the average molecular weight thereof is preferably 1,000W 20,000.