Polymer concrete is a relatively new type of concrete in which polymer is used as a binder. This paper investigates the effect of compositions on the tensile strength and mode-I fracture toughness of polymer concrete (PC) and fiber-reinforced polymer concrete (FRPC). According to the literature, the range of compounds (in unit weight) is selected 15 to 25% for resin, 0 to 2% for fibers, 45 to 55% for fine aggregates, and 25 to 35% for fine and coarse aggregates. Using a design of experiment software, 198 specimens made of 66 different mixture designs have been designed, prepared, and tested. The results show that reducing the size of aggregates, increasing fiber content, and increasing resin content increase the tensile strength and fracture toughness. Results show that fiber reinforcement effect on mixtures with higher resin and smaller aggregates content is more promising. In addition, the minimum resin content for PC and FRPC materials is about 12.5%. In addition, the results show that the optimal percentage of fiber depends on the percentage of resin; in a mixture with 15%, optimum resin content is equal to 1.5%, and in a mixture, with 25%, optimum resin content is equal to 4.0%.