PURPOSE: To provide the titled recording material capable of forming a color in high density and having excellent preservation stability, wherein a thioester derivative having a specified melting point is used as a color forming assistant together with a diazonium salt, a coupler compound and a color developer.

CONSTITUTION: In a fixable-type thermal recording material wherein a photosensitive thermal layer comprising a diazonium salt, e.g., 2,5-diethoxy-4-morpholinobenzenediazonium tetrafluoroborate, a coupler compound, e.g., 2-hydroxy-3-naphthoic acid 2'-ethoxyanilide, a color forming adjuvant and a particulate dispersed material of an organic basic compound giving a basic atmosphere by being melted when being heated, e.g., a compound of formula I , as a color developer is provided on a base, a thioester derivative of formula II, wherein each of R1 and R2 is H, chain or cyclic alkyl or aryl, and each of X and Y is O or S, having a melting point of 40W160°C, preferably, 70W135°C, e.g., S-(4-bromophenyl)monothiobenzoate, is used as the color forming assistant, preferably in an amount of 0.1W20 times by weight with regard to the diazonium salt.