Abstract: Located in the middle of Yunnan Plateau,as the second deepest lake in China,Fuxian Lake is being polluted.Tradescantia micronucleus frequency were determinated in 10 water samples obtained from different sites of Fuxian Lake,and the mutagensis of the water samples of the lake were estimated.The results showed that the water along the shores of the lake was much more polluted than that in the central area of the lake,and the water in the southern part of the lake was more contaminated than that in the northern part of the lake.