Novel bisphthalonitrile-terminated bismaleimide-containing monomers (BMIPNs) were synthesized from 4-aminophenoxy phthalonitrile and various phenylene diamine (ortho, meta and para)-based bismaleimides (BMIs). The chemical structure of the ortho-, meta-and para-substituted bismaleimide-containing phthalonitrile-terminated monomers (o-BMIPN, m-BMIPN and p-BMIPN) were confirmed by FTIR, H-1-NMR and C-13-NMR analysis. The curing behavior of the different monomers was investigated by FTIR and DSC analysis with 5 wt% of diaminodiphenylsulfone as curing agent. Thermal polymerization of the synthesized monomers (BMIPNs) results in the formation of crosslinking network structures. The thermal decomposition behavior of all the cured BMIPN polymers (BMIPNPs) was examined by thermogravimetric analysis in N-2 atmosphere. All the cured polymers showed excellent thermal stability. The 5 (T-5%) and 10 % (T-10%) weight loss temperatures of the polymers were ranging from 389 to 440 and 431 to 488 degrees C, respectively. The char yield of the ortho-, meta-and para-substituted BMIPNPs improved significantly from 60 to 70 wt%. Dielectric measurements of the BMIPNPs show slight variation with frequency. All the polymers exhibit very good moisture-resistant properties.