AbstractEffects of gamma radiation and the marble particle size on compressive properties and the dynamic elastic modulus of polymer concretes (PCs) were studied. The PCs had a composition of 30 % of unsaturated polyester resin and 70 wt. % of marble as aggregate. Different types of PC were developed with the combination of one, two or three marble-particle sizes. The materials were submitted to 5, 10, 50, 100 and 150 kGy of radiation doses. Both the compressive properties and the dynamic elastic modulus values depend on the combination of the marble-particle sizes and the applied radiation dose. Higher numbers of dispersed particles per unit volume provide more resistance to crack propagation. On the other hand, longer particles give more reinforcement. As a result of these two competing effects, medium size marble particles provide the highest compression modulus