A heat sensitive recording material having a recording layer formed on a substrate and containing a colorless or light-colored basic dye and a color acceptor, the heat sensitive recording material being characterized in that at least one ethyleneimine derivative of the following formula (1) is contained in the recording layer as a preservability improving agent for record images ##STR1## wherein R.sub.1 is direct bond, --O--, --S--, --SO.sub.2 -- or C.sub.1 .about.C.sub.6 alkylene, R.sub.2 and R.sub.3 are each C.sub.1 .about.C.sub.4 alkyl, C.sub.1 .about.C.sub.4 alkoxyl or halogen atom, m and n are each zero or an integer of 1 to 4.