PURPOSE: To improve preservation stability of a recorded image by a method wherein a heat-sensitive color layer containing a dyestuff precursor, a specified developer reacted with the precursor during heating to color the precursor, and a sulfoamide compound are formed on a sheet-form substrate.

CONSTITUTION: In a heat-sensitive recording substance used for an image recording sheet, a vehicle ticket, various labels and cards and forming a color image by heating, a heat-sensitive color layer containing an achromatic or hypochromic dyestuff precursor and a developer reacted with the dyestuff precursor during heating to color it is formed on at least one surface of a sheet substrate. At least one kind of a compound having at least one arylsulfony ureide, represented by a general formula described at the right, wherein R is an unsubstituted aromatic group or a lower alkyl group, in one molecule is contained as the developer. Further, at least a sulfonamide compound represented by a formula of Ar1-SO2NH-Ar2 is contained.