In this research work, the effect of carbonization on the flexural strength, hardness, water absorption and density of coconut shell/unsaturated polyester composite was studied. A portion of the coconut shell was carbonized at 700^oC in a heat treatment furnace with a soaking time of three hours while the other portion was uncarbonized. They were ground and sieved into two particle sizes. Flexural strength, hardness, density and water absorption properties of the developed composites were determined. The 30wt% of the 1700microns uncarbonized coconut shell particle reinforced composite sample absorbed more water. Maximum flexural strength was obtained at 20wt. % for the 425microns sample reinforced composite while that of hardness was at 30wt.%. The density of the composite decreased with increase in filler content. The SEM showed the distribution of coconut shell particles within the composite. The carbonized coconut shell particle reinforced composite recorded the least density value, therefore, this composite can be used in applications requiring light weight material.