Abstract: A bacterial strain Pseudomonas sp． SY-6 was immobilized in sodium alginate． The optimal preparation conditions for the strain immobilization were investigated by the experiments and its degradation characteristics were studied． The results showed that when the concentration of sodium alginate was 4%，the concentration of CaCl2 was 3% and immobilized time was 4h，the mechanical strength and the mass transfer performance of obtained immobilized beads were the best and was qualified to degrade nicosulfuron． The optimum pH，initial temperature and inoculation of nicosulfuron degradation by strain SY-6 were 7. 0，30℃ and 5%，respectively． The immobilized bacteria could tolerate pH and temperature in a wider range than the free bacteria． The sequencing batch reactor ( SBr) was used for nicosulfuron wastewater treatment and the results showed that the strain was stable in treating nicoslfuron wasterwater in appropriate usage cycles，which would provide the foundation for the engineering application of the immobilized beads of nicosulfuron degradation strain．