The isothermal cure behavior of an unsaturated polyester resin system is studied by differential scanning calorimetry. The reaction heats (at different curing temperatures) are presented and compared to the results of the previous studies. Various kinetic parameters as well as details of the curing process can be obtained and elucidated, based on the Avrami theory. The experimental results reveal that this analytical method is valid for describing the curing behavior of unsaturated polyester resins.