A partially purified beta-fructofuranosidase from Aspergillus japonicus was covalently immobilized on to chitosan beads using either glutaraldehyde or tris(hydroxymethyl) phosphine (THP) as a coupling agent. Compared with the glutaraldehyde-immobilized and the free enzyme, the THP-immobilized enzyme had the highest thermal stability with 78% activity retained after 12 days at 37 degrees C. The THP-immobilized enzyme also had higher reusability than that immobilized by glutaraldehyde, 75% activity was retained after 11 batches (or 11 days) at 37 degrees C for the THP immobilized enzyme system. Less yield (48%) of fructooligosaccharides ( FOS) were produced by the THP-immobilized enzyme compared with the free enzyme system ( 58%) from 50% (w/ v) sucrose at 50 degrees C.