A fast scanning calorimetric method to obtain the time and temperature dependence of the glass transition temperature (T-g) under a chemical reaction was reported. The cross-linking reaction of an epoxy-amine system is perfectly suppressed by an ultrafast temperature scan. By inserting the quenching and fast heating measurements in an isothermal or non-isothermal process, the quasi-real-time change in T-g during cure can also be obtained from a single piece of neat resin. In addition, the relation between T-g and conversion is obtained in a full range of conversion by combining with the conventional analysis of isothermal or non-isothermal reaction kinetics using differential scanning calorimetry or temperature modulated differential scanning calorimetry.