Cotton, sponge and alginate-Ca as immobilized matrix were used in the biological treatment of heavy metal wastewater. The effects of the different immobilized matrix and the growth of synechococcus sp. were studied. The effects by the cotton and sponge were not good, despite of a high growth rate and a long life of synechococcus sp obtained with cotton. Alginate-Ca was the best immobilized matrix. The results showed that the different density of alginate-Ca makes the different removal efficiency to the heavy metal, alginate-Ca showed high efficiency to the heavy metal during the longer period of treatment time .