The curing behavior of vinyl ester resin containing unmodified and functionalized graphene nanoplatelets (GNP) was studied by means of differential scanning calorimetry at various curing temperatures. The temperatures of exothermic heat flow, which were derived from the curing reaction of vinyl ester resin, were detected in the range of 70~115˚C, 120~155˚C and 160~190˚C, respectively, regardless of the absence and presence of GNP. The exothermic peak area for vinyl ester resin containing the functionalized GNP was higher than that for neat vinyl ester resin and the unmodified GNP. For clarifying this behavior, the activation energy of neat vinyl ester resin and the GNP-containing vinyl ester resin was calculated by the Friedman method. The analytical result indicates that the curing behavior depends on the functionalization type of GNP as well as on the presence or absence of the GNP. Keywords: Vinyl ester resin, Curing behavior, Graphene nanoplatelets, Differential scanning calorimetry.