Enzyme immobilization has attracted great interest in biotechnology processes. Herein we report the immobilization of urease from Canavalia ensiformis (jack bean) in sol-gel-derived silica nanocomposites. Urease activity, differential scanning calorimetry (DSC) nitrogen and water adsorption isotherms were used to characterize the effect of storage at various relative humidities on enzyme activity immobilized in sol-gel-derived silica nanocomposites. In this study, the nanocomposites consist of tetraethoxysilane, as inorganic silicate precursor, in combination with glycerol or trehalose as organic additives. Entrapped urease was more stable for all the formulations aged with a relative humidity of 80%. However, significant differences (p < 0.05) in enzyme activity recovered at this relative humidity were observed between samples with different formulations, reflecting the effect of additives during the immobilization process. The applications of biocompatible sol-gel-derived matrices can be further extended and utilized in the development of biosensors with immobilized biomolecules that can be used for long time periods by taking into account different factors, among which the storage relative humidity has permitted to greatly improve the stability of the immobilized urease. (c) 2008 Elsevier Inc. All rights reserved.