Abstract:The effect of exogenous cholesterol on the fluidity of mitochondrial membrane from riceroot apex was investigated using the DPH fluorescece probe (1,6-diphenyl-l, 3, 5,-hexatriene).Results showed that exogenous cholesterol, either being absorbed by root system during water culture of rice or being added directly to the prepared mitochondrial of control rice root apex, decreased the fluorescence intesity of probe in the mitochondrial membrane and reduced the fluorescence polarization as well as micro-viscosity, but increased the fluidity of the mitochondrial membrane in rice root apex.