Nanocomposites have been obtained by intercalation of preformed negatively charged guest La hydroxy citrate colloids into host Mg/Al layered double hydroxides (LDH). These compounds have been used as precursors for La/Mg(Al)O mixed oxides catalysts. The La loading has been controlled by the colloids exchange rate in order to achieve a better dispersion of the lanthanum cations and thus improve the basic properties of the new catalysts. The increase of the d(003) interlayer distance from 0.830 nm in the host LDH to 1.196 nm in the nanocomposites shows that the intercalation has taken place leading to 1.82-11.16 wt% of lanthanum cation loadings. The basic properties of the La/Mg(Al)O(x) mixed oxides were evaluated qualitatively using Hammett indicators and quantitatively by TPD of CO2. Both techniques indicated the presence of strong basic sites. The transesterification of 1-phenylethanol with diethylcarbonate (DEC), which is known to involve strong basic sites, was used to evaluate the catalytic activity of the La/Mg(Al)O(x) mixed oxides. Yields into carbonate product increase with the density of strong basic sites of the catalyst. (c) 2010 Elsevier B.V. All rights reserved.