Repeated-batchh and continuous production of L-lactic acid by immobilized Rhizopus oryzae with calcium alginate entrapment method in a three-phase fluidized-bed bioreactor was studied. The operation conditions were optimized. The productivity based on total reactor volume was about 3 times higher than that with free cells in a traditional stirred tank bioreactor. A mathematical model was proposed and the model predictions were in good agreement with the experimental data.