This paper presents the development of quasi-fixable thermal paper, where the color forming capability of the non-imaged part (or the white portion) is considerably reduced by simply heating the thermal paper for a few seconds (fixing operation) after the imaging operation.The use of the word “Quasi-” is because the fixed part can not be made completely unreactive, but still becomes slightly colored when high heat is applied. Nevertheless, the image on this thermal paper can be recognized or read even after heat-ironing the paper at as high as 180°C (360F).The images can be formed easily as those on the conventional thermal paper, and the images are highly stable because of employing a sulfonyl urea dye-developer.