Design of polymer concrete involves extensive studies on their materials in order to get improved properties; specifically on the physicochemical properties of both polymer resin and mineral aggregates, including size and shape of the last one. Alternative studies are focusing on using different materials or methods to obtain such improvements. In this work, polymer concrete was elaborated with unsaturated polyester resin, marble particles and polypropylene fibres, after it was modified by using gamma radiation to achieve a complete polymerization. The results show improvements in the compressive strength and in the modulus of elasticity with 0.2 vol.% of polypropylene fibres and irradiation at a dose of 250 KGy. However, lower compressive strains were obtained when using gamma radiation.