AbstractA 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), 1H‐ and 13C‐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∼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).