Bismaleimide (BMI) resins with good thermal stability, fire resistance, low water absorption, and good retention of mechanical properties at elevated temperatures, especially in hot/wet environments, have attracted more attention in the electronic and aerospace industries. However, their relatively high dielectric constant limits their application in the aforementioned fields. In this work, a new promising approach is presented that consists of the formation of a self-catalytic thermoset/ thermoset interpenetrating polymer network. Interpenetrating polymer networks (IPNs) based on modified BMI resin (BMI/DBA) and cyanate ester (b10) were synthesized via prepolymerization followed by thermal curing. The self-catalytic curing mechanism of BMI/DBA-CE IPN resin systems was examined by differential scanning calorimetry. The dielectric properties of the cured BMI/DBA-CE IPN resin systems were evaluated by a dielectric analyzer and shown in dielectric properties-temperature-log frequency three-dimensional plots. The effect of temperature and frequency on the dielectric constant of the cured BMI/DBA-CE IPN resin systems is discussed. The composition effect on the dielectric constant of the cured IPN resin systems was analyzed on the basis of Maxwell's equation and rule of mixture. The obtained BMI/ DBA-CE IPN resin systems have the combined advantages of low dielectric constant and loss, high-temperature resistance, and good processability, which have many applications in the microelectronic and aerospace industries. (C) 2003 Wiley Periodicals, Inc.