[en] Curing rate is the variation rate of degree of cure with time, which is a crucial issue in the curing process of composite structures since it has a significant influence on the generation of voids and residual stresses. In this paper, an online monitoring method of degree of cure was presented based on refractive index measurement. The influence of cure and temperature variation on the refractive index of composite was separated in real time with a step-temperature refractive index separation method. Non-isothermal microwave curing process of carbon fiber/epoxy composite was monitored, and the degree of cure was obtained with a low measurement error of ±1.5% compared with that determined by off-line DSC measurement. The online monitoring method is a promising technology for smart manufacturing of composite structures. (paper)