Cure behavior of a catalyzed epoxy/anhydride system was investigated for an epoxy-rich formulation using differential scanning calorimetry (DSC). The mixture was isothermally cured at different times and temperatures, and the cure behavior of the samples was analyzed by the peak exothermic temperature (T-peak) and the extent of cure reaction (X) from DSC thermograms. For the excess epoxy sample, two exothermic peaks at a low temperature from esterification reaction and at a high temperature from etherification on DSC curves appeared in the early stage of cure and shifted to a lower temperature scale with curing. However, the esterification peak disappeared and the remaining etherification peak shifted to a higher temperature with further cure. The shift of the peaks may be attributed to the change of reaction mechanism from kinetically controlled to diffusion-controlled. The extent of cure of esterification and etherification was also considered separately in this article. The result shows that esterification reaction mainly occurs in the early stage of cure and then etherification slowly proceeds after the completion of the esterification.