AbstractThe aim of this study is to characterize the state of progress of a polymerization reaction by a non‐destructive electric method. For this purpose, results deduced from measurements of complex permittivity are compared with those obtained from chemical analysis of the reaction mixture at successive instants of its evolution. Chemical analysis allows the rate of disapperace of expoxy groups during the polymerization reaction in liquid phase to be evaluated. Exploitation of electric measurements of complex relative permittivity enables the evolution of the polymerization to be followed from both the product of the epoxy group concentration and the square of the mean value of their dipole moment and also from the most probable relaxation time of this dipole. As expected, the variations of relaxation time are closely correlated to those of the viscosity of the mediu