Electrospun polyvinyl alcohol (PVA) fibers are used to immobilize lipase entrapped in organosilicate cages. The cages are prepared from dimethyldimethoxysilane and tetramethoxysilane (called Fiber-SilicaLip in this paper) and are Used as the active component of a flow-through reactor for the continuous production of fatty acid butyl esters by butanolysis of rapeseed oil. The catalytic activity of the catalyst, defined by reaction rate during the first 4 h of reaction, depended on the content of water in the mixture of rapeseed oil and n-butanol (molar ratio of triglyceride and n-butanol = 1 :3). The highest catalytic activity was detected at 0.5% (w/w) water addition. At this level, Fiber-SilicaLip showed a 57-fold increase in catalytic activity over purchased lipase powder and 3.7-fold higher catalytic activity than PVA fibers enclosing non-treated lipase. In addition, the reaction rate per amount of catalyst (matrix + protein lipase) detected at 0.5% (w/w) water addition was 1.6 times greater than the maximum value detected for Novozym 435 with no added water. The Fiber-SilicaLip continued to work as a catalyst for a 14 clay run as a membranous component of a continuous fatty acid butyl esters production system. (C) 2009 Elsevier B.V. All rights reserved.