Polymer concrete (PC) was developed by using different concentrations of silica sand as aggregate and a commercial unsaturated preaccelerated (orthophtalic) polyester resin. The PC specimens were submitted to gamma radiation at several dosages: 5, 10, 50, 100, and 150 kGy. Mechanical performance was evaluated including the compressive strength, the compressive strain at yield point, and the compression modulus of elasticity. As expected, mechanical properties depend on both the resin concentration and the applied radiation dose. Improvement achieved in mechanical properties is related to the morphological characteristics observed by scanning electron microscopy.