A new family of polymer, namely hyperbranched thermosetting poly(imide-ester) (HBPIE), was successfully prepared by the esterification reaction between a hyperbranched oligoimide terminated with carboxylic end groups (-COOH) and a hyperbranched oligoester terminated with acetoxy end groups (-OAc). The hyperbranched oligoimide has a degree of branching of one, M-w = 14 180, and polydispersity Pd = 1.953. The -OAc-terminated oligoester has M-w = 7000 and polydispersity Pd = 1.17. The NMP solution of the oligoimide and oligoester had excellent film-forming properties. HBPIE films cured from these two oligomers are thermally stable and display surface area of 83 m(2)/g due to their intrinsic microporosity (pore size 12.7 Angstrom). The submicrometer thin film of HBPIE also displays an intermediate dielectric constant and high dielectric breakdown strength.