The cure monitoring of composite parts is an important key to optimize the industrial curing cycles. In this study, it is proposed to monitor the cure of a thermosetting resin by a Fresnel refractometer. The measurements are first compared to dielectric analyses and predictions of a thermo-kinetic model that uses parameters from the literature. Under isothermal conditions, the results show that the Fresnel power can be directly exploited to obtain qualitatively the degree of conversion. This is also demonstrated in anisothermal conditions by correcting the Fresnel signal from its temperature dependence. If the initial degree of conversion is known, its quantitative assessment is achieved using the Fresnel and temperature measurements. POLYM. ENG. SCI., 54:626-635, 2014. (c) 2013 Society of Plastics Engineers