PURPOSE: To improve the colorific performance and long term stability of the thermal recording body concerned by a method wherein thermal colorific layer contains specified compound, which has one or more specified aryl sulfonyl ureido groups per one molecule as developer, and specified compound having sulfonamide group as sensitizer.

CONSTITUTION: In the thermal recording body concerned, at least on one side of sheet-like base, thermal colorific layer is provided. The thermal colorific layer contains colorless or light-colored dye precursor and developer, which reacts under heat with the dye precursor so as to color the dye precursor. In this case, the developer contains compound having one or more aryl sulfonyl ureido groups, which are represented by the general formula as noted elsewhere, per one molecule. Further, the thermal colorific layer contains at least one of sulfonamide compounds, which are represented by the other general formula as noted elsewhere and different from p-toluenesulfoanilide and benzenesulfoanilide. Thus, the colorific performance of the thermal recording body and, at the same time, various durabilities and long term stabilities of colored image are improved.