To study the regularities of reticulocyte's membrane shear elastic modulus and membrane viscosity, a model of anemia in rabbits induced by injection of phenylhydrazine was established. Using a new ektacytometry, the small deformation index (DI)_d and the half-time (t_0.5) for deformation relaxation of the reticulocytes under the abnormal physiological conditions were measured. (DI)_d and t_0.5 were respectively put into the reticulocytes membrane shear elastic modulus (E) formula and the membrane viscosity (μ_m) formula. Through calculation, the value of E and μ_m in the process of reticulocytes changing into erythrocytes in vivo for 72 h were obtained. It was found that the membrane shear elastic modulus and membrane viscosity decreased in this process of changing. This finding had some basic theoretical and clinical significance.