The behavior of phase separation during the curing reaction of unsaturated polyester (UPE) resin in the presence of low profile additive, that is, poly(vinyl acetate) (PVAc), was studied by low-angle laser light scattering (LALS) and scanning electron microscopy (SEM). The experimental results revealed that the PVAc-rich phase was regularly dispersed in the cured styrene-UPE matrix for styrene-UPE resin blended with 5 wt % of PVAc. As the PVAc content was increased higher than 10 wt %, a cocontinuous PVAc and cured styrene-UPE phase was observed for the cured systems. The LALS observations were carried out in situ at a curing temperature of 100 degrees C; thus, the effect of the rate of exothermic heat released from curing reaction on the morphology of curing system was investigated and reported in this work.