Allelopathy, the release of extracellular compounds that have an effect on the growth of other microorganisms, may be one factor contributing to formation and/or maintenance of cyanobacterial blooms. In this paper, the allelopathic effect between single-cell Microcystis aeruginosa and three filamentous cyanobacteria Aphanizomenon. flos-aquae, Anabaena flos-aquae, Phormidium, mucicola was investigated. The experiment was conducted to find out the allelopathic effects of cell-free filtrate on the growth of different target organisms: 1. the cell-free filtrate of M. aeruginosa on Aphanizomenon flos-aquae, Anabaena flos-aquae and P. mucicola; 2. the cell-free filtrate of Aphanizomenon, flos-aquae, Anabaena flos-aquae and P. mucicola on M. aeruginosa. The results demonstrated that M. aeruginosa could accelerate the growth of Aphanizomenon flos-aquae and Anabaena flos-aquae, and slightly inhibited P. mucicola. On the other hand, the growth of M. aeruginosa was slightly suppressed by Aphanizomenon flos-aquae and Anabaena flos-aquae, but heavily inhibited by P. mucicola. The inhibition by P. mucicola, was enhanced with the increase of concentration of cell-free Filtrate. Furthermore, the allelopathic effect between single-cell M. aeruginosa and three filamentous cyanobacteria Aphanizomenon flos-aquae, Anabaenaflos-aquae, P. mucicola was not influenced by the change of the concentration of inorganic nutrients in cell-free filtrates. It suggests that the inter-species competition existed in cyanobacteria. The present study is implicated in illustrating dynamics of the cyanobacterial bloom.