Ion exchange behavior of organic anions of differing sizes and structures, including carbonate ions and dodecyl sulfate ions, with Mg/Al layered double hydroxide (LDH) was quantitatively investigated. The effect of the type and amount of organic anions taken up on the structure and surface properties of the LDH was also examined. Ion exchange isotherms of the Langmuir type were obtained for the uptake of C6H5COO-, C2O42-, CH2(COO)(2)(2-) and C6H4(COO)(2)(2-) in the LDH. With these anions, uptake reached 71-88% of the theoretical ion exchange capacity of the LDH. The differences in uptake amount are thought to derive from differences in valency and ion size among them. The ion exchange isotherm of LDH for C12H25OSO3- was also of the Langmuir type, and the uptake amount almost equaled the theoretical ion exchange capacity. The interlayer distance of LDH was found to vary with uptake of organic anions, corresponding to the orientation of anions in the LDH structure. The contact angle of LDH containing dicarbonate ions with water was only slightly larger than that of NO3- type LDH, the starting material before anion exchange. This means that the LDH surface is hydrophilic after the uptake of dicarbonate ions. Conversely, C12H25OSO3- gave the largest contact angle, that is, the most hydrophobic surface among the organic anions used.