We have investigated the feasibility of developing polysulfone (PS) membranes to partially immobilize Pseudomonas and to evaluate the inhibitory effect of phenol on immobilized Pseudomonas by monitoring their growths in partially immobilized cell and free-suspension systems. The polysulfone membranes used in this study were wet spun from 20 wt % of PS in 1-methyl-2-pyrrolidone (NMP) solvent using water as the bore fluid as well as the external coagulant. Scanning electron microscopy (SEM) characterization of the newly developed PS hollow fibers suggests that fiber crosssection consists of multilayer microporous structures useful for cell immobilization. Experiments were conducted using Pseudomonas bacteria to remove phenol with initial phenol concentrations of 300 mg/L and 1000 mg/L. In a free suspension (no membrane) system, it was observed that the bacteria were able to grow optimally at 300 mg/L of phenol and degraded phenol almost completely in about 26 h. However, neither cell growth nor phenol degradation occurred when initial concentration of phenol was increased to 1000 mg/L. In a cell-immobilized membrane system, the cell growth and phenol concentration profile in the medium were very similar to those obtained in a free-suspension culture if phenol concentration was 300 mg/L. However, when the initial phenol concentration was increased to 1000 mg/L, data obtained in a cellimmobilized membrane system was discernibly different from that obtained in the suspension culture. In the former case, phenol concentration decreased in the beginning of the test, indicating that the carbon source has been consumed and immobilized cells within the membrane had begun to multiply. As soon as the phenol concentration decreased to about 600 mg/L (at which concentration, substrate inhibition was not as severe as 1000 mg/L), partial immobilization occurred when some cells diffused out of the membrane into the medium and optical density became measurable in the medium. It was found that cell growth continued for the next 28 h, reaching a maximum optical density in the medium of 0.610 absorbance units, and phenol was also completely degraded.