Abstract: Effect of fluoride on the surfacelayer fluidity was determined by fluorescence polarization technique using ANS as fluorescence probe in vitro in order to further understand the mechanism of cellular effect and membrane toxicity of fluoride.When exposure doses of fluoride from 8 to 32 mmol/L,the fluorescence polarization of ANS in erythrocyte and liver cell membrances was not increased significantly,but the surfacelayre fluidity of synaptic membrane was decreased obviously with negative doseeffect relationship.The results suggest that the effect will be of great significance in membrane toxicity and neurotoxicity of fuoride.