The curing behavior and thermomechanical properties of dicyanate/polyethersulfone (PES) blends were investigated. Differential scanning calorimetry (DSC) was used to study the curing behavior of the dicyanate/PES blends. A second-order autocatalytic reaction mechanism was used to describe the cure kinetics of the blends. The reaction kinetic parameters were determined by fitting DSC conversion data to the kinetic equation. The main glass-transition temperatures of the blends decreased with increasing PES content. Two glass-transition temperatures indicating phase-separated morphology of the blends were observed. The thermal decomposition behavior of the blends was measured using thermogravimetric analysis. Mechanical and electrical properties of the blends were investigated.