Erythrocyte orientation and deformation cause differences in impedance between flowing and resting blood. Through theoretical calculation and experimental measurements, we studied the effects of these factors on blood impedance. The size and shape of the erythrocyte and the conductivity of the interior medium of the erythrocyte change when the osmotic pressure of plasma is changed. From experimental results, we obtained the following: when the size of the erythrocyte becomes larger than the normal size due to the osmotic pressure change, the β dispersion frequency decreases and the intra- and extracellular fluid resistance increase. These experimental results corroborate that the change of tissue impedance like muscle impedance during hemodialysis is caused by the change of the fluid distribution and the change of ionic concentration of the electrolyte in tissues during hemodialysis. Also, we could estimate the relative change value of the intra- and extracellular fluid volume by the impedance method, if there were no ionic concentration change in the electrolyte. It would be very difficult to estimate the absolute change value of them because a shadow effect due to the cells depends greatly upon the shape and size of the cells and the cell concentration.