A curing agent Thiourea-diethylenetriamine (TU-DETA) was successfully prepared with its structure characterized by Fourier transform infrared spectrum and nuclear magnetic resonance (C-13-NMR spectrum). The curing agent TU-DETA contained incompletely reacted material diethylenetriamine (DETA) and the polymerization degree (n) of TU-DETA was equaled to either 1 or 3 according to liquid chromatography-mass spectrometry (LC-MS) analysis. Kinetics of thermal degradation of DGEBA (diglycidyl ether of bisphenol A)/TU-DETA epoxy system was investigated with thermogravimetric analysis (TGA) under non-isothermal conditions with heating rates of 5, 10, 12.5, 15, and 20 degrees C/min. The derivative thermogravimetry curves of DGEBA/TU-DETA epoxy system revealed that the thermal degradation process was only a single weight-loss step. The apparent average activation energy calculated with the Flynn-Wall-Ozawa method was 140.4 kJ/mol. With a combination of the Coats-Redfern and Phadnis-Deshpande methods, it was showed that the most probable mechanism of degradation process of the cured epoxy resin was F1 deceleration type.