This research was carried out to investigate the effect of particle size on the flexural strength, ultimate tensile strength, density and water absorption characteristics of uncarbonized coconut shell/unsaturated polyester composite. Two particle sizes of 425micron (fine Sample UFS) and 170microns (coarse Sample UCS) of uncarbonized coconut shell particles were used as reinforcement. Flexural strength, ultimate tensile strength, density and morphological properties of the developed composites were determined. Maximum flexural and ultimate tensile strengths were both obtained at 20wt. % for the 425microns sample reinforced composite. The 30wt% of the 425microns coconut shell reinforced composite sample absorbed more water. The density of both composite particle sizes decreased with increase in filler content indicating use in applications requiring light weight.