Recently, the alloys of polyurethane (PU)/polybenzoxazine (PBA-a) have been studied due to many interesting properties; however, the thermal degradation kinetics of the system has not been mentioned before. In this study, the degradation temperatures of the obtained alloys were determined using Thermogravimetric Analyzer (TGA) with various heating rate of 10, 20, 25oC/min. The polyurethane /polybenzoxazine alloys at the weight ratios of 30/70 were prepared for determination due to its highest degradation temperature. The first derivative curves of the thermograms (DTG) were deconvoluted with Peak-fit program. The results reveal three main sub-stages of degradation. According to Arrhenius Eq., the activation energies (Ea) of each degradation sub-stage were determined using Kissinger model and Fynn-Wall Ozawa model.