In the conversion of D-sorbitol to L-sorbose by immobilized Gluconobacter suboxydans cells, the diffusion of oxygen through immobilized beads was found to be a limiting factor. This observation was based on the activation energy value estimated from an Arrhenius plot of the reactions at various temperatures. The L-sorbose yield was increased when bead size was reduced and holes were made in the beads as a means of reducing the thickness of the oxygen diffusion layer. However, some diffusion difficulty remained. When beads which were co-immobilized with the oxygen-carrier n-dodecane were used for the reaction, the oxygen uptake rate and the L-sorbose yield were both increased, indicating that enhanced diffusion of oxygen in beads produces an increase in the L-sorbose yield. The yield in a fluidized bed reactor filled with n-dodecane co-immobilized beads was increased by 48 and 20%, respectively, at aeration rates of 2 and 6 vvm. The activation energy value estimated from the reactions using n-dodecane co-immobilized beads indicates that the overall reaction was kinetically controlled. When perfluorodecalin was added directly to the reaction medium the diffusion of oxygen from bulk to the bead surfaces was hindered, resulting in a reduction of L-sorbose yield.