In the present study, fire reaction improvement of an epoxy polymer mortar (PM) formulation, induced by polymer modification with three different flame retardant (FR) systems, was analyzed and quantified. For this purpose, several epoxy PM formulations, modified with different contents and/or types of phosphate, metal hydroxide and brominated based FR systems, were manufactured and tested for both, fire reaction and flexural strength. The results were compared with those of plain epoxy PMs. Fire reaction of PM formulations was assessed by means of the Oxygen Consumption Calorimeter test, also known as Cone Calorimeter test. This test allows the determination of the main parameters that assess fire reaction behaviour of combustible materials: heat release rate, smoke extinction area, carbon dioxide and monoxide release rates, and ignitability. Test results revealed that all FR systems, in particular the phosphate based one, are effective in improving fire reaction performance of epoxy PMs. Moreover, this improvement is attained without significant losses of bearing carrying capacity of PM materials.