To investigate the effect of diffusional limitations on the cure of thermosetting polymers, a modeling strategy has been developed for estimating the average diffusion coefficient of the molecular species in the curing systems. The modeling is based on the dielectric measurement of the mobility-related properties including the ionic conductivity and the dipole relaxation time. It was shown that the ionic conductivity is the dominant factor in the diffusion model valid in the pregel stage, while the dipole relaxation time may be utilized to evaluate the diffusivities in the postgel stage. This approach may find applications in the study of the diffusion-controlled cure kinetics and structure-property relationships in thermosetting polymer systems.