A facile synthesis of a new class of reactive porous materials is reported: hierarchically porous hydrogen silsesquioxane (HSiO1.5, HSQ) monoliths with well-defined macropores and mesopores. The HSQ monoliths are prepared via sol-gel accompanied by phase separation in a mild condition, and contain micrometer-sized co-continuous macropores and high specific surface area reaching up to 800 m2 g−1 because of the small mesopores. A total preservation of Si–H, which is always an issue of HSQ materials, is confirmed by 29Si solid-state NMR. The HSQ monolith has then been subjected to reduction of noble metal ions to their corresponding metal nanoparticles in simple aqueous solutions under an ambient condition. The nanoparticles produced in this manner are immobilized on the HSQ monolith and are characterized by X-ray diffraction (XRD) and high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Both the bare HSQ and nanoparticles-embedded HSQ are promising as heterogeneous catalysts, exhibiting reusability and recyclability.