The effects of low-profile additives(LPA), poly(vinyl acetate)(PVAc) on thecuring of unsaturated polyester(UP) resins at 100oC were investigated by usinga defferential scanning calorimeter(DSC), light scattering(LS) and scanning electron microscopy(SEM). The behavior of phase separation during the curing reaction of unsaturatedpolyester in the present of low- profile additives, i.e. poly(vinyl acetate),was studied by light scattering(LS) and scanning electron microscopy(SEM). Theexperimental results revealed that for styrene / UP blended with 5% wt of PVAc, PVAc-rich phase was separated and dispersed in UP matrix phase. As thePVAc content was incresed higher than 10% wt of PVAc rich phase was separatedand dispersed in UP matrix phase in the middle of curing reaction. After the final stage of curing(close to vitrification) co-continuous PVAc and UP phaseoccured.