The object of research is a composite material obtained based on MGF-9 polyester-acrylate resin with quartz sand as a filler. Samples were prepared using a curing system consisting of PKOH-2 cyclohexanone peroxide and OK-1 cobalt octoate. Method. Physical experiment. The compressive strain was performed on a Shimadzu Autograph AG-X universal testing machine. To process the results, differential methods were used: calculation of the effective modulus and the rate of change of mechanical parameters. According to the obtained graphic dependences, an analysis of the change in mechanical parameters was carried out, a comparison was made with samples not filled with quartz sand. Results. The nature of the change in the effective modulus depending on the degree of deformation and the magnitude of mechanical stress during deformation of the composite and pure resin differ significantly, which indicates the difference in the molecular processes occurring in them. It is shown that the hysteresis loss in the composite is usually less than in the resin without filler. As in unfilled samples of polyester acrylate, the greatest change in the state of the material occurs in the first loading cycle.