The amount of marble dust occurred during machining and cutting of marble pieces and fly ash emitted from coal power plant is rather high and these wastes create significant environmental pollution. In fact, these wastes can be utilized in various industrial applications. In this study, various amount of fly ash, marble dust and polyester as base material, methyl ethyl keton peroxid as hardener and cobalt naphtanats as accelerator were used to produce polyester matrix composite material. Mechanical properties of composite materials were investigated and the optimum values were determined. In the first step of the manufacturing of composite material, the amounts of hardener, accelerator and polyester were kept constant and only fly ash/marble dust ratio was changed. The experimental results showed that while fly ash/marble dust ratio up to 1/3 was increased, the strength and hardness of the composite materials increased. Thus, the composite materials with high strength and hardness were produced. The optimum three point bending strength and hardness values were 30.42 N/mm2 and 98 Shore A, respectively. In the second step, the amounts of hardener, accelerator and fly ash/marble dust ratio were kept constant and the effects of the change in the amount of polyester were investigated. It was seen that the highest tree point bending strength and hardness were obtained at polyester/filler (marble dust +fly ash) ratio of 0,38. The optimum three point bending strength and hardness values were 32.78 N/mm2 and 99 Shore A, respectively.