Abstract: N-phenyl maleimide modified novolac resin was synthesized by condensation polymerization of a mixture of N-phenyl maleimide and formaldehyde by slowly feeding phenol in the presence of an acid catalyst. The polymerization conditions were optimized to obtain the high reaction conversion of PMI and proper viscosity of PPMF. It was found that reaction competition and conversion ratio for PMI were enhanced with increasing feeding time of phenol. As the reaction reflux time was increased, the conversion of PMI and the viscosity of PPMF were increased. At a higher reaction temperature or more amount of PMI, the conversion of PMI was decreased. The resins were characterized by FTIR, 13C NMR and thermal analysis. It was found that the N-phenyl maleimide groups were combined in the chains of novolacs and the N-phenyl maleimide content of PPMF could reach around 33%. DSC curve revealed two curing peaks,of which one at around 150℃ was attributed to the condensation reaction of methylol groups formed in minor quantities on the phenyl rings,and the other at around 250℃ was attributed to the addition curing reaction of the maleimide groups. TGA analysis showed that the cured PPMF had better thermal properties.