Abstract: This paper describes,the preparation and properties of polymer-supported liquid membrane immobilized cells of Arthrobacter simplex which catalyze the transformation of cortisol into predni-solone.The transforming activity of cells immobilized by this method was compared with that of cells immobilized by traditional entrapment method.The result showed that the transforming activity of the former was obviously higher than that of the latter,and there was no apparent difference of mechanical strength between che former and the latter under our working conditions.The various factors affecting the transformation were studied as well.