PXRD (powder x-ray diffraction), FT-IR (Fourier Transform infrared), N-2 adsorption at 196 degrees C and TG/DTA (thermogravimetric and differential thermal analyses) techniques have been used for characterisation of MgAl- and ZnAl-CrO4 LDHs, which had been prepared by the ion exchange method from the corresponding chloride LDH (layered double hydroxides) precursors. The results indicates that the oxometalate intercalation in both systems produces interlayer microporosity and a basal spacing of 8.7 angstrom; This gallery height decreases when the samples are calcined in the temperature range 100-300 degrees C, due to a grafting process. A larger thermal stability is detected for MgAl-CrO4 sample than for the zinc-containing one.