There appears to be a correlation between pore size and thermal stability of hydrotalcites samples doped with M 2+ metals: all samples with small pores, which we attribute to small agglomerates of primary crystallites (HT 65, Ni HT65, Ni HT80, Cu HT 65) also exhibit superior thermal stability for loss of interlayer carbonates. This may be a result of similar physical phenomena controlling both, thermal stability and the crystallites agglomeration rate.