We evaluated the influential factors of the activated sludge capable of phenol decomposition immobilized on photo-crosslinked resin. The immobilized activated sludge showed a broader range of pH and higher relative activity than the free activated sludge. The optimum pH on the degradation of phenol in both free and immobilized activated sludge was 7. When the pH of the reaction was varied from 5 to 10, the relative activity of the phenol degradation by the immobilized activated sludge was higher than that by the free activated sludge. A higher rate of phenol degradation was observed when a bead size was smaller. Continued treatment of immobilized activated sludge showed more than 95% of phenol removal under 5.59 kg-phenol/m³'d of load, which is twice as large as the load with free activated sludge.