The microstructure in cured resins decides their mechanical properties. An important characteristics in cured vinyl-ester resin is micro-gels and bi-phase structure．The morphological structure of cured vinyl-ester resin and the formation of two-phase structures in vinyl-ester resin has been studied by using SEM and differential scanning calorimetry (DSC)．The results demonstrated the existence of clusters of gel-particles with a size of about 20 μm

each cluster of gel-particles containing many gel-particles with coral-like structures．The formation of gel-particles resulted in two-phase structure characterized by the two peaks in the rescanned DSC thermographs of the resin. The cure conditions (temperatures

post-cure) affected microstructure in the cured resins．The results of mechanical properties showed that the cure conditions affected the mechanical properties．The post-cure for the sample isothermally cured at 80℃ increased the tensile strengths and flexural strengths．On the contrary

the post-cure for samples isothermally cured at 120℃ decreased the tensile strengths and flexural strengths．