The objective of this research was to study the possibility of blending unsaturated polyester resin (UPE resin) with 5, 10, and 15 parts per hundred resin (phr) natural rubber latex (NRL) in the presence of dispersion aids in order to improve the impact resistance of UPE resin. Three types of dispersion aids, sodium lauryl sulfate (SLS), toluene, and ammonia, were used in this study in amounts of 10, 15, 20 and 25 wt % of the NRL. These blended mixtures were cured at room temperature using methyl ethyl ketone peroxide (MEKPO) as an initiator and cobalt octoate as an accelerator. It was found that, regardless of the type of dispersion aid, the impact strength of blended UPE samples was higher than that of the pure UPE samples, and at 20 wt % toluene in 15-phr NRL, the sample had the highest impact strength. However, because of low elastic modulus, characteristic of NRL, the tensile strength and flexural strength of the blended samples decreased as the NRL content of the blends increased. (c) 2006 Wiley Periodicals, Inc.