Flyash is an inexpensive material that can reduce the overall cost of the composite if used as a filler for unsaturated polyester resin (PR). Flyash-filled unsaturated polyester resin(FPR) was cast into sheets. The tensile strength, flexural strength, and flexural modulus were determined. Calcium carbonate-filled polyester resin(CPR) and PR were also cast into sheets. The above-mentioned properties were determined and a comparison was made. The filler concentration was varied from 0 to 15 wt %. it was found that FPR was inferior to CPR and PR composites with respect to tensile and flexural strengths. But FPR was found to have a higher flexural modulus than those of CPR and PR. FPR with 10% flyash was found to have poor acid and solvent (benzene) resistances and good saltwater, alkali, weathering, and freeze-thaw resistances as seen from the mechanical properties. The possible ways of improving the strength of FPR are discussed.