Abstract: It is the first report on Cyanophage isolated from Lake Taihu and infected Microcystis aernginosa (M. aernginosa). Water samples were collected from Lake Taihu during bloom season. The water sample was filtered through 0.22 μm polycarbonate membranes and concentrated by tangential flow fitration system, and then was inoculated into exponentially growing cultures of M. aernginosa strains. A further research was done for the algae with obvious infection. The results showed that M. aernginosa 905 was lysed. The lysate was purified through the method of CsCl density gradient centrifugation and one-step growth curve for the cyanophage was also studied. When MOI was 10-5, the latent phase of cyanophage infecting M. aernginosa was 2 hours, the rise phase was 4-6 hours and stabilization was 6-12 hours. The burst size was 4 pfu/cell. The virion with an icosahedral head (nearly 50 nm in diameter) and a short tail was observed under the transmission electron microscopy. The cyanophage had not only the specificity of species but also the specificity of strains. It could only infect M. aernginosa 905. In addition, the infection activity was lost when the cyanophage was stored at -20 an℃ d -80℃ without cryoprotectants, but the infection activity maintained over 50 days at 4℃. The above findings provide a potential method for biological control of algae bloom by cyanophage.