Pre-impregnated fibers (prepregs) are one of the biggest challenges for material recycling. In this study, production-derived prepreg waste in amounts ranging from 0.1 vol% to 5.0 vol% was incorporated as reinforcement in an epoxy-based polymer concrete. The effects of prepreg content and aggregate ratio (sand-to-gravel) on the mechanical (flexural and compressive strength), structural and physical properties of the polymer concrete were evaluated. The thermal properties of the resin within the prepreg waste were investigated, alongside its bonding capability with the epoxy resin employed in polymer concrete production. A prepreg content of 3.0 vol% resulted in an approximate 50% increase in both flexural and compressive strength, attributed to structural reinforcement by short fibers. However, higher prepreg contents led to a marked increase in open porosity (from 0.17% to 6.22%) and, consequently, in water absorption at 5.0 vol% prepreg, which is undesirable. Statistical analysis identified the optimal prepreg content and aggregate ratio as 3.0 vol% and a 35:35 sand-to-gravel ratio, respectively.