The bismaleimide (BMI)-modified novolac resin was synthesized by allylation of the novolac resin and its "Ene" reaction with BMI. The reactions were monitored by Fourier transform infrared analysis (FTIR). The morphology of the BMI-modified novolac resin changed with degree of allylation (i.e., the amount of BMI used). On the basis of the studies done by dynamical mechanical analysis (DMA), differential scanning calorimetry (DSC), and field emission scanning electron microscopy (FE-SEM), it was found that when the degree of allylation increased from 48 to 59%, the resin changed from a single-phase structure to a two-phase structure. From the research by thermogravimetric analysis (TGA) and DMA, it was found that the higher allyl-content (when > 48%) caused a decrease of the thermal properties and mechanical properties of the resultant resin. The BMI-modified allyl novolac resin with 48% degree of allylation has the best thermal properties and the highest dynamic modulus in the current research. (c) 2006 Wiley Periodicals, Inc.