Abstract: Cyanate esters were modified by carboxyl terminated liquid butadiene-acrylonitrile (CTBN) to improve theirtoughness. Optimized curing parameters were obtained by gel time curves and differential scanning calorimetry (DSC) ofthe systems. Fourier transform infrared spectrometry (FTIR) and DSC were employed to show the curing behavior of thesystems. It was observed , by comparison with purified cyanate esters , that the addition of CTBN has large influence onthe curing behavior of the systems during lower temperature , but little during higher temperature. Scanning electron microscopy (SEM) was employed to show the micro properties of the cured matrixes ; mechanical properties and dielectricproperties of the cured resin were measured. It showed that when 15 % CTBN was added to CE , the best modified systemwas gotten ; its flexural strength and impact strength were increased 39.47 % and 21.92 % , respectively. Additionally , asshown in the TGA curves of the systems , with the increasing content of CTBN from 0 to 15 % , the thermal degradationtemperature decreased from 407 ℃to 383 ℃.