Electrospun fibrous membranes composed of poly(vinyl alcohol) (PVA) fibers of approximately 1 mu m in diameter, and immobilizing highly activated lipase entrapped in silicate cages with smaller dimensions than the fibers, were developed: and their feasibility as a component of flow-through reactors was studied. The electrospun PVA fibers were prepared from a mixture of PVA solution and a sol obtained from silicon alkoxide(s)-either tetramethoxysilane (TMOS) or dimethyldimethoxysilane (DMDMOS), or both, containing lipase. The fastest initial transesterification rate converting (s)-glycidol to glycidyl n-butyrate with vinyl n-butyrate in batchwise reactions was accomplished by treatment of lipase using the sol obtained from DMDMOS and TMOS together. The values were 4.5-,21.8-, and 1.8-fold faster than those of systems using lipases that were either non-modified or modified using TMOS alone or DMDMOS alone, respectively. The higher activity of the lipase modified using both DMDMOS and TMOS and immobilized in PVA fibers resulted in a flow-through reactor having a higher degree of conversion at the same retention time compared with that using immobilized non-modified lipase. These results show the feasibility of flow-through reactors composed of electrospun PVA fibers immobilizing lipase highly activated by alkyl-silicate. (c) 2008 Elsevier B.V. All rights reserved.