A hyperbranched, functional, and biocompatible polymer, poly(epsilon-caprolactone)-grafted hyperbranched polyester (HPCL), was synthesized via a facile two-step routine as a prospective nontoxic, biodegradable, and biocompatible drug delivery system. H-1-NMR measurements provided direct evidence that epsilon-caprolactone was grafted by a reaction with the peripheral functional hydroxyl groups of hyperbranched polyesters. pH-responsive HPCL in different synthetic body fluids (SBFs) could controllably incubate aspirin. In the different SBFs, the release rates were diverse. In SBF with a pH of 7.4, the release time was nearly 110 h, whereas in SBF with a pH of 6.4 and SBF with a pH of 7.8, it was 185 and 71 h, respectively. In comparison with previously reported systems, our system had a longer release life. (c) 2008 Wiley Periodicals, Inc.