New aromatic bismaleimides containing bis(phenoxy)naphthalene unit, were synthesized. They were prepared by reacting a diamine-containing naphthalene and maleic anhydride by the usual two-step procedure that included ring-opening addition to give bismaleamic acid, followed by cyclodehydration to bismaleimide. The monomers were characterized by infrared (IR), proton nuclear magnetic resonance (H-NMR), elemental analyses (EA), and mass spectra (MS). Their thermal polymerization was investigated by differential scanning calorimetry (DSC). The presence of a naphthalene group in the backbone of the bismaleimide had increased the curing temperature and reduced the reactivity of the maleimide bond. The glass transition temperatures of the polymers were in the range of 291-334 degrees C. Thermogravimetric analyses of the cured resins showed higher thermal stability and char yield for naphthalene-containing bismaleimides than for the corresponding benzene analog. The observed char yield of the bismaleimide resins are in accordance with the calculated C/H ratios.