Saccharification of alpha-amylase liquefied cassava starch was carried out at pH 4.5 and 45 degrees C, in both fixed and fluidized bed reactors, using amyloglucosidase immobilized in 0.5 mm controlled pore silica particles. Reactor performance data are compared with mathematical modeling. Data show that for equal normalized residence time and lower fluid-bed porosities, the fluidized bed mode leads to higher conversions than fixed bed. Interparticle mass transfer experiments showed absence of diffusion limitations and starch conversion reached 98.5% with a real residence time of only 10 min, whereas the conventional liquid-phase process requires 48 h to achieve the same conversion.