Uniformly dispersed graphene oxide (GO)/cyanate ester (CE)-epoxy (EP) composites were successfully synthesized by in situ polymerization. Both the results of FT-IR and XPS verified that epoxide groups on the GO sheets reacted with cyanate group (O-C equivalent to N) in the resin. These results could provide excellent dispersion of GO and strong interfacial interaction between GO and CE matrix. TEM confirmed that GO tended to be a single layer. XRD and SEM indicated that matrix molecules could be inserted into the interplanar spacing of GO. The mechanical properties and thermal behavior of the composites were investigated in detail. It is observed that GO reinforced EP-CE composites demonstrated improved mechanical properties and better thermal stability than that of EP-CE matrix, which make them suitable for use in aerospace applications and structural composites. (C) 2014 Elsevier B.V. All rights reserved.