The first example of synergistic alkynyl-tin initiated ring-opening polymerization of cyclic ester in the presence of nanotubular silica particles is herein reported. Hydroxyl groups on the halloysite (HNTs) surface act as initiators for caprolactone polymerization and the resulting polymers are covalently grafted to the HNTs. The covalent anchorage of the poly(ε-caprolactone) (PCL) backbone to the HNTs ensures a high degree of interpenetration at the hybrid interface thereby allowing long-term stability of the PCL-grafted-HNTs suspension. Scanning electron microscopy analyses showed the uniform dispersion of the HNTs filler within the PCL matrix. The melt viscosity of the poly(ε-caprolactone)/HNTs composites decreases with increasing clay content. Thermal stability and microindentation hardness properties of the resulting nano-composites were significantly improved, as compared to native, non-reinforced PCL.