Cyanotoxins produced by cyanobacteria have caused pollutions in land surface water around the world.The most common toxin is microcystin,a cancer inducing hepatoxin.Microcystin is chemically stable in water and can't be effectively removed by conventional water treatment processes. Microbiological removing,especially bacterial degrading was an effective way to eliminate microcystins from water. In this research,Cyanotoxin degrading bacterium strain S3 and Chlorella elldpsodea LI were co-immobilized by sodium alginate to degrade microcystin-LR (MC-LR).Results showed that the alga could increase the growth of strain S3 in the gel beads. The coimmobilined bacteria had a higher degrading efficiency of MC-LR than independent immobilized cell. The degrading efficiency ofimmobilized cells was influenced less than the free cells when temperature and pH changed.When the immobilized cells were reused, they could maintain high degrading efficiency.