Mixing induced by wind-wave is one of the important factors in lake ecosystems. To understand the effects of mixing induced by wind-wave on colony size of Microcystis in lake, an in-situ experiment was conducted in Lake Taihu. The results showed that the colony size of Microcystis in treatments with wind wave for 24 h and in control was 68.38 and 12.56 μm, respectively. There was a significantly difference between them. The extracellular polysaccharides concentration of Microcystis in treatment with mixing continuing for 24 h was 1.49×10^-6 mg/cell, which was significant higher than that in control(1.26×10^-6 mg/cell). The results suggested that appropriate intensity of mixing induced by wind-wave can significantly enlarge the colony size of Microcystis in a short time. It will helpful to understand the mechanism of the Microcystis blooms in Lake Taihu.