A diazonium salt represented by the following general formula (1) and a thermal recording material using the diazonium salt:General Formula (1) ##STR00001## wherein R.sup.1 and R.sup.2 each independently represents an alkyl group, an aryl group, an acyl group, an alkoxycarbonyl group or a carbamoyl group, and R.sup.1 and R.sup.2 may be linked each other to form a ring; and R.sup.3 to R.sup.6 each independently represents a hydrogen atom, a hydroxyl group, a halogen atom, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, an alkylsulfonyl group, an arylsulfonyl group or a diazonio group, and at least one of R.sup.3, R.sup.4, R.sup.5 and R.sup.6 represents the diazonio group.