Studies on the curing reactions of epoxy systems were carried out in the presence of a cellulose derivative, hydroxypropyl cellulose (HPC). The technique of differential scanning calorimetry (DSC) was applied to characterize the curing reactions/thermal properties. Classical nonisothermal kinetic methods, such as the Kissinger and the Osawa methods (multiple scan) and the Barrett method (single scan) as well as the recently one proposed by Samios et al., were applied to study the reaction kinetics of the epoxy system of diglycidyl ether of bisphenol A (DGEBA) and 4,4'-diaminodiphenylmethane (DDM) with HPC. The Barrett method gives additional information about the process of initiation, gelation, and vitrification. At the beginning of the epoxy curing reaction, HPC acts as a catalyst so that the energy of activation diminishes and the reaction occurs at lower temperatures. Above the minimum temperature T-min, it was concluded that HPC behaves as an inhibitor of the reaction (T-min, is the temperature which corresponds to the minimum point showed by the exotermic peaks during the curing reaction of an epoxy resin measured by DSC). By analyzing the behavior of the kinetic parameters, Ea, k, and ln A, the molecular interactions were shown to be related to the catalyst-inhibitor characteristics of HPC.