The coordination-insertion ring-opening polymerization of epsilon-caprolactone was initiated from amine or hydroxyl groups spread over the surface of silica (ca. 30 nm) or cadmium sulfide (ca. 1.5 nm) nanoparticles, respectively. The initiation selectively occurred from the surface functional groups after activation into aluminum alkoxides species. The covalent grafting of the polyester chains was confirmed by the solubilization of the nanoparticles in organic solvents, e.g., CHCl3 and THF for silica nanoparticles and toluene for CdS nanoparticles, at least when the surface-grrafted PCL chains were long enough. In the case of silica nanoparticles, the linear dependence of the PCL molar mass as determined by H-1 NMR analysis on the initial monomer-to-amine ratio confirmed the controlled character of the polymerization. Transmission electron microscopy of thin films of PCL-grafted CdS revealed an homogeneous dispersion of the semiconducting nanoparticles throughout the polyester matrix.