PURPOSE: To prevent the deterioration of a background during storage, by obtaining a fixable thermal recording material wherein one of a diazo sulfonate compound and a coupling component is included in a capsule.

CONSTITUTION: Diazo sulfonate or a coupling component is dissolved or dispersed in an org. solvent insoluble in water to be emulsified with said solvent. A microcapsule is formed by a method wherein a core substance containing diazo sulfonate or the coupling component is emulsified to form oil droplets and a wall comprising a high-molecular substance is formed at the periphery of each oil droplet. The reactant forming the high-molecular substance is added to the interior or exterior of the oil droplet. The thermal recording material obtained by adopting this method can be widely used, for example, as the printing paper of a facsimile or an electronic computer requiring high speed recording. By decomposing unreacted diazo solfonate by exposure fter thermal printing, a formed image can be fixed.