A new bismaleimide (BMI) resin system, designated 4504, with excellent heat resistance and good mechanical properties for advanced composites was developed. The 4504 resin was made up of 4,4’-bismaleimidodiphenyl methane, diallyl bisphenol A, and desirable catalysts. The reactivity of 4504 was investigated by gel characteristics and differential scanning calorimetry (DSC). Data showed that 4504 had a long work life under 100 degrees C, but would gel within 7 min or 40 s at 140 or 160 degrees C, respectively. The glass transition temperature (T-g) and heat-deflection temperature (HDT) of the cured 4504 resin were 315 and 290 degrees C, respectively, which were much higher than the postcure temperature (200 degrees C). In addition, the cured resin is also tough. Thermogravimetric analysis (TGA) in a nitrogen atmosphere revealed that the neat resin was stable up to 450 degrees C; its char yield at 700 degrees C under anaerobic conditions was 29.4%. Carbon fiber T300 laminates based on 4504 were prepared and characterized. In the case of short-beam (SBS) strength, when tested at 230 degrees C, 51% of the original room temperature strength was retained.