In the preparation of conventional polymer-modified mortars using epoxy resin, the use of any hardener has been considered indispensable for the hardening of the epoxy resin. The authors have noticed that the hardening of epoxy resin occurs in the presence of alkalis in cement mortar. Polymer-modified mortars using epoxy resin without any hardener are prepared with various polymer-cement ratios, and tested for strength, adhesion, water absorption, drying shrinkage, chloride ion penetration and carbonation. From the test results, the polymer-modified mortars using the epoxy resin without any hardener are made successfully, and have some superior properties compared with conventional epoxy-modified mortars. It is concluded that polymercement ratios of 5 to 10% are considered optimum for the preparation of such polymer-modified mortars.