The metal catalyzed ring-opening polymerization Of D,L-lactide monomer inside the nanometer-sized channels of MCM-41 and SBA-15 hosts, creating an organic-inorganic hybrid polymeric material, is described. Detailed characterization of the polylactide/mesoporous silica organic-inorganic composite by multiple spectroscopic, microscopy, and calorimetric methods, as well as solvent extraction, reveals that the resulting in situ synthesized composite is unique relative to physical or solution-cast mixtures of polylactide and the mesoporous host. In this contribution, we focus on the incorporation of the stannous octanoate (Sn2+) catalyst inside the mesoporous host channels prior to monomer introduction and Subsequent polymerization and specifically target the differentiation of polymerization chemistry that Occurs inside the host channels versus less desirable reactions on the exterior surface of the mesoporous host crystallites.