Abstract: A stabilized glucose isomerase concentrate is prepared by contacting an aqueous mixture containing cell-free glucose isomerase and a water miscible organic solvent such as 2-propanol with a magnesium salt to form an enzyme-magnesium precipitate. The cell-free glucose isomerase may be prepared by mixing cells containing intracellular glucose isomerase with the water miscible organic solvent and digesting the cells with a lysozyme enzyme preparation. The stabilized concentrate contains magnesium and the water miscible organic solvent, and retains at least about 95% of its initial isomerase activity when stored at 26.degree. C for up to 30 days and about 80% of its initial isomerase activity when stored at 18.degree. C for up to one year.