Abstract: The symptom, conditions of pathogen development, modes of infection, and damage extent of the red-ring disease to blue-green algae are studied. The results indicated that the optimal physical conditions of the pathogensis of red-ring disease are similar to those of the maximal growth of blue-green algae. The pathogenic bacterium infects blue-green algae through the culture medium of diseased algae and/or through pathoge-carrying algal (fresh and dry algae)inoculum. The disease lysed blue-green algae seriously and decreased the production of biomass. The comprehensive measures for the prevention and control of red-ring disease are discussed.