Abstract: Immobilized cells wese used, in fluidised bed, for the degradation of LAS in waste water. The degradating process was theoretically analyzed, and its kinetic model was studied tentatively. The experimetal result in dicales that the degradation rates of LAS obey Monod equations in the concentration rang of 20-100 mg/L. Also, the maximum reation rate r_s,max and the substrate constant k_s were determined in Monod. These data can be Applied to the designing of piliot scale and full-scale bioreactors.