Abstract: The invention relates to a novel water-insoluble glucose isomerase which is formed by a crystalline enzyme converted to solid form by cross-linking. The invention also concerns a process for the preparation of the novel crystalline glucose isomerase by cross-linking with dialdehyde in the presence of a compound containing at least one amino group, and the use of this novel enzyme preparation as an isomerization catalyst. Preferrably the compound having an amino group is an ammonium salt, lysine or tryptophan and the dialdehyde is glutaraldehyde.