Abstract: Experiments in two groups of rabbits (supine and head-down 20°) were done to observe the effects of cephalad redistribution of body fluid during simulated weightlessness on rabbit's ear microcirculation.Results showed that cephalad redistribution of body fluid can induce certain changes in microcirculation,i.e.increase of bore of capillaries and veinles,decrease of flow speed and blood pooling in veins,aggregetion of blood cells,patechae in the ears,and changes of regulative function of the microvessels during orthostasis.The indexes of blood rheology also had relative changes.The cause of certain changes were analysed,and some new ideas were postulated.A kind of specially designed rabbit cage and the method of observation of microcirculation through intact rabbit ears were also introduced.