A new phosphorus-containing polycyclic bismaleimide resin (BMPI) was prepared by the reaction of bis(3-maleimidophenyl) methylphosphine oxide (BAMP) with benzene-1,2,4,5-tetracarboxylic dianhydride (BTD) and maleic anhydride (MA). BMPI was confirmed by infrared (IR), H-1- and C-13-NMR spectroscopies. Its thermal properties were carried out by a differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) that revealed that the polymers have excellent thermal properties in the high temperature region and a high char yield of up to 53 similar to 65%. Furthermore, three conventional bismaleimide resins were prepared from different phosphorus-free bismaleimides for comparison, e.g. 4,4'-bismaleimidodiphenylmethane (BDM), 4,4'-bismaleimidodiphenylether (BDE), 4,4'-bismaleimidodiphenylsulfone (BDS).