Fly ash is a byproduct of coal-fuel burning process in thermal power plant. It is removed from the plant exhaust gases primarily by electrostatic precipitators, or baghouses and secondarily by scrubber systems. Fly ash is generally light tan in color and consists mostly of silt-sized and clay-sized glassy spheres. This gives fly ash a consistency somewhat like talcum powder. Fly ash is a pozzolan, a siliceous material which in the presence of water will react with calcium hydroxide at ordinary temperatures to produce cementitious compounds. Because of its spherical shape and pozzolanic properties, fly ash is useful in cement and concrete applications. This paper shows the results of study on the effect of fly ash on mechanical properties of polymer composite materials based on unsaturated polyester resin. The results showed that the use of fly ash increasing the mechanical strength of polymer composite materials (composite reinforced fly ash) compared to non-fly ash composites.