Nanoporous poly(methyl silsesquioxane) (PMSSQ) thin films were successfully prepared using a new thermally sacrificing porogen, dimethylamino-functionalized polyhedral oligomeric silsesquioxane (DMA-POSS). The core-shell silsesquioxane was synthesized from Acrylo POSS with 3-dimethylaminopropylamine (DMAPA) and 2-dimethylamino ethyl acrylate (DMAEA) using Michael addition reaction. Miscible hybrid materials were obtained through strong hydrogen-bonding interaction between the Si-OH end group in MSSQ and the tertiary amino groups in DMA-POSS. Nanopores in PMSSQ matrix were generated by thermal decomposing DMA-POSS at 425 degrees C. The AFM and FESEM studies suggested that nanopores were homogeneously distributed in the prepared thin films. As the porosity increased up to 16.4%, the refractive index and the dielectric constant of the nanoporous films were decreased from 1.379 to 1.307 and 2.8-2.2, respectively. The tertiary amino substitutes could promote the silanol condensation and improve the mechanical properties. Therefore, the hardness retained around 1 GPa as the porosity increased. The low-dielectric constant, good thermal and mechanical property suggested the potential applications of these films as low-dielectric constant materials. (C) 2008 Elsevier B.V. All rights reserved.