High-performance hyperbranched poly(phenylene oxide)-modified bismaleimide resin with high thermal stability, low dielectric constant, and loss was developed, which is made up of hyperbranched poly(phenylene oxide) (HBPPO), 4,4'-bismaleimidodiphenylmethane (BDM), and o, o'-diallylbisphenol A (DBA). The curing reactivity, morphology, and performance of BDM/DBA/HBPPO resin were systemically investigated, and similar investigations for BDM/DBA resin were also carried out for comparison. Results show that BDM/DBA/HBPPO and BDM/DBA resins have similar curing mechanism, but the former can be cured at lower temperature than the later; in addition, cured BDM/DBA/HBPPO resin with suitable HBPPO content has better thermal stability and dielectric properties (lower dielectric constant and loss) than BDM/DBA resin. The difference in macroproperties between BDM/DBA/HBPPO and BDM/DBA resins results from the different chemical structures and morphologies of their crosslinking networks. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 451-457, 2011