Abstract: Pseudomonas aeruginosa which can grow with p-nitrophenol as sole carbon and nitrogen sources was immobilized in sodium alginate. Optimal preparation condition of the strain immobilization was determined by the cross-test experiments, and the effects and influencing factors of immobilized cells technique on the degradation of p-nitrophenol studied. The results show that the degradation efficiency of immobilized cells is apparently superior to that of free cells. The tolerant concentration of immobilized cells is higher than that of free cells. The optimal pH of degrading p-nitrophenol is 8.0-9.0, and the optimal temperature is 30-35 ℃. The removal rate of p-nitrophenol at the concentration of about 50 mg/L approaches 100% after 42 h. The curve of the kinetics of the degradation can be divided into two parts. The first part is lag period from zero hour to 35 hours and the second part is from 35 hours to 42 hours. p-nitrophenol can be degraded rapidly within 7 hours with the growth of the strain. Immobilized cells can be used to degrade p-nitrophenol repeatedly and continuously for three times and can keep steady degradation ratio.