The effect of the size and surface area on the ion conductivity of layered double hydroxide (LDH) containing Mg2+ and Al3+ intercalated with CO32- was investigated, with a focus on particles smaller than 100 nm. The size of LDH was controlled by changing the pH during coprecipitation and the hydrothermal treatment time. The ion conductivity increased with the decrease in the crystallite size and the increase in the specific surface area. We thus found that surface conduction greatly contributed to the total ion conduction for small-size LDH, in addition to the interlayer conduction previously proposed as the dominant conduction mechanism in LDH. (C) 2012 Elsevier B.V. All rights reserved.