The enzymatic reaction mechanism of fructooligosaccharide production from sucrose was investigated by use of a beta-fructofuranosidase from Aspergillus japonicus Competitive product inhibition by glucose was observed from kinetic analysis for the substrates sucrose, 1-kestose, and nystose. In addition, the reaction rate of sucrose was inhibited at concentrations greater than 20% (w/v). A mathematical model was proposed based on the kinetic observation to simulate fructooligosaccharides production from sucrose. The mathematical calculation agreed with the experimental data for the initial sucrose concentrations of 30% (w/v) and 50% (w/v) at 37 degrees C.