The behavior of dipalmitoyl phosphatidylcholine bilayers in CaCl2 aqueous solution found by Inoko et al. (Biochim. Biophys. Acta 413, 24(1975)) is analyzed, with four states I-IV appearing with increasing concentrations of CaCl2 from 0 mM to 1 M. The present theory takes into account the field-dependent association constant K of Ca2+ ions to the membrane surface, which was derived from a theoretical investigation (Y. Izumitani, J. Colloid Interface Sci. 166, 143 (1994)) of the electrostatic cation-dipole interaction, The present theory is based on the DLVO theory of colloid stability, which was also used in the analysis of this phenomena by Ohshima and Mitsui (J. Colloid Interface Sci. 63, 525 (1978)), but in the present theory, the transition of states I --> II is conditioned by the membrane flexibility and the retardation effects are taken into account in the van der Waals interaction in the lamellar structure. The discrepancy between the observed values for the repeat distance of the lamellar phase and the theoretical predictions of Ohshima’s theory can be fairly well explained by the present theory with state III at 10-100 mM CaCl2 concentration. The undulation effect is neglected in our treatment but the membrane flexibility can qualitatively explain the hysteresis in the I-II transition.