The present study was focused on elucidating the effects of nanopore diffusional resistance on the activity of Burkholderia cepacia (BC lipase) lipase immobilized in ordered mesoporous silica hosts. BC lipase was immobilized in ordered SBA-15 hosts possessing 55 and 240 angstrom diameter pores by physical adsorption. A colorimetric assay of p-nitrophenyl acetate was employed to determine the lipase catalytic activity. The effect of diffusional resistance on catalytic activity of lipase immobilized in SBA-15 hosts was investigated by determining the effective substrate diffusivity as a function of pore size of the SBA-15 host and enzyme loading. Lipase immobilized in SBA-15-55 angstrom exhibited 20-30% of free lipase activity and the activity was further reduced with enzyme loading due to limited accessibility of substrate to the enzyme active sites. Lipase immobilized in SBA-15-240 angstrom hosts showed catalytic activity similar to free lipase activity suggesting that diffusional limitations were minimal. Large pore SBA-15 hosts provided an improved environment for BC lipase to retain its catalytic activity. (c) 2008 Elsevier Ltd. All rights reserved.