THERMAL RECORDING SHEET

PROBLEM TO BE SOLVED: To provide a thermal recording sheet which shows high development sensitivity, high heat resistance, no dusting phenomenon overt time and the inhibited deterioration of a developing density even after a long time of conservation of a color undeveloping part. SOLUTION: In the thermal recording sheet with a heat-sensitive developing layer composed mainly of a colorless or pale color basic colorless dye and an organic color developer formed on a support, the heat-sensitive developing layer contains 4-hydroxy-4'-n-propoxydiphenylsulfone as the organic color developer and also a sulfonamide derivative expressed by formula. In the formula, Z is a 1-6C lower alkyl group or an electron-attractive group. n is an integer of 0-2. In addition, the blending ratio of 4-hydroxy-4'-n-propoxydiphenylsulfone to sulfone amid derivative is 1:0.1-1:3.