Sol-gel condensation of tetramethoxysilane (TMOS) inside the channels of a coordination pillared layer structure [Cu-2(pzdc)(2)(dpe)]n (1a; pzdc = pyrazine-2,3-dicarboxylate, dpe = 1.2-di(4-pyridyl)ethylene) produced subnanosized silica dispersed within the host framework. In this system, the growth of silica is effectively constrained, and the resultant silica shows a drastic decrease of its crystallization temperature because of its minute size.