Fixable thermosensitive recording sheet

A fixable thermosensitive recording sheet consisting of a substrate, a photo- and thermo-sensitive layer composed of an acid stabilized diazonium salt capable of forming a dye by reacting with a coupler compound, and a heat-softening binder material, said layer being formed on said substrate, and a developer layer composed of a heat-softening binder material and a particulate dispersion of a heat-fusible developer capable of supplying a necessary amount of base for allowing said acid stabilized diazonium salt to react sufficiently with the coupler compound, said developer layer being formed on said photo- and thermo-sensitive layer, wherein the coupler compound is contained in at least one of said two layers and the heat-fusible developer is a hydrophobic guanidine derivative represented by the general formula:

• ##STR4## wherein one or both of R.sub.1 and R.sub.2 is/are selected from the group consisting of alkyl, cycloalkyl, aryl and aralkyl groups, and when only one of R.sub.1 and R.sub.2 is selected from said groups, the remaining R.sub.1 or R.sub.2 is hydrogen;
• one or both of R.sub.3 and R.sub.4 is/are selected from the group consisting of alkyl, cycloalkyl, aryl and aralkyl groups, and when only one of R.sub.3 and R.sub.4 is selected from said groups, the remaining R.sub.3 or R.sub.4 is hydrogen;
• and R.sub.5 is selected from the group consisting of alkyl, cycloalkyl, aryl and aralkyl groups, wherein said cycloalkyl group may have a halogen substituent and said aryl group may have a substituent selected from the group consisting of alkyl, alkoxy, nitro and halogen.