Abstract: The bisphenol A epoxy resin (E51) and bisphenol A cyanate (BCE) were used as the raw materials to study the co-curing reaction kinetics mechanism. At the same time, E51-BCE was used as the matrix resin, and Al₂O₃ obtained with Sol-Gel method as reinforcement to prepare the Al₂O₃/E51-BCE composites. The solidification process and curing kinetics of the system were determined by non-isothermal DSC, and the apparent activation energy of the system are 66.13 kJ/mol and 69.46 kJ/mol according to the Kissinger and Ozawa equation, respectively. Infrared spectroscopy was used to track the reaction route of the system at the initial curing temperature of 160℃ and 180℃. The results reveal that E51 reacts directly with BCE when the curing temperature starts at 160℃. The BCE's reactivity will be improved when the curing temperature is 180℃, BCE is mainly consumed in the self-polymerization reaction, and the formation rate of the triazine ring is accelerated. A little part of BCE directly reacts with E51 to form an oxazoline structure. The FTIR and TEM results of Al₂O₃ show that the structure of Al₂O₃ is a short fiber-like crystal with a little amount of hydroxyl groups on its surface. The SEM patterns of the Al₂O₃/E51-BCE composites indicate that Al₂O₃ presents as disperse phase in matrix, the interface between Al₂O₃ and matrix is fuzzy and the failure cracks are irregularity, thus it is typical ductile fracture. 3wt% Al₂O₃ is uniformly dispersed in matrix, and the impact strength and bending modulus of Al₂O₃/E51-BCE composites is 24.2 kJ/m² and 2.54 GPa, respectively, which are increased by 53.65% and 22.12% compared with E51-BCE matrix resin. The mechanical properties of Al₂O₃/E51-BCE composites are improved obviously.