Osmotic shock is clinically widely used to measure erythrocyte health. In order to analyze the fragility of erythrocytes, effects of factors such as osmotic pressure, hydrostatic pressure, and membrane tension on the swelling and shrinking processes must be examined. Hypotonic shock-induced swelling experiments were performed on erythrocytes under a non-hemolytic condition. Erythrocyte swelling was modeled using a one-dimensional model in which the osmotic difference across the membrane was obtained by solving diffusion equations for the inner and outer regions of the erythrocyte membrane. The simulated timewise changes in erythrocyte volume and osmotic difference fitted well with those of the experiments when the permeability coefficient of the membrane was adjusted. In the simulation, the time to swell to a sphere was almost the same as that in the experiment, and the non-hemolytic condition was satisfied, as the membrane tension was smaller than a hemolysis inception tension. By changing the area expansion modulus of the membrane, the differences in erythrocyte diameter, after being spherical in the equilibrium state, were calculated and then compared. The diameter differences were too small to be resolved with an optical microscope. However, the estimated time differences to reach hemolysis were measurable, suggesting that mechanical characterization of the area expansion modulus of the membrane is possible.