Purification of glucose isomerase by its partitioning in a PEG-salt aqueous two-phase system (ATPS) in the presence of PEG derivatives has been studied. Selective partitioning of the proteins was observed towards the PEG phase containing PEG-benzoate and PEG-palmitate, enriching glucose isomerase in the salt phase. Cross-current extraction in 4 stages in the presence of PEG-palmitate gave an enrichment factor of similar to 5 for the enzyme. After initial purification with ATPS, glucose isomerase was immobilized on cross-linked chitosan beads. The immobilized enzyme was stable over a wider pH range (5.2-9.0) and showed an optimum pH of 6.5.