Layered double hydroxides(LDHs) with hydrotalcite type structure containing Fe 3+ , Al 3+ and Mg 2+ were prepared by means of a coprecipitation method. The products were characterized by element analysis, X ray powder diffraction and transmission electron microscopy. It was found that even if the molar ratio of n (Fe+Al) / n (Fe+Al+Mg)>0 33, yet a pure hydrotalcite like compound(HTlc) phase was gained when n (Fe)/ n (Al+Mg+Fe)≤0 30 and n (Al)/ n (Al+Mg+Fe)≤0 30; the Al(OH) 3 phase appeared in the products when n (Al)/ n (Al+Mg+Fe)>0 30; and an amorphous phase emerged when n (Fe)/ n (Al+Mg+Fe)>0 33. These results show that there is no concentration superposition effect between Fe 3+ and Al 3+ on the crystalline state of the produced samples. In our previous work, the concentration superposition effect between Zn 2+ and Mg 2+ in the synthesis of Zn Mg Al LDHs was found. For the prepared Fe Al Mg LDHs samples, the value of lattice parameter a is between 0 30-0 32 nm; and the value of lattice parameter c is between 2 30-2 47 nm, the basal spacing is in the range of 0 76-0 83 nm. When the ratio of n (Fe)/ n (Al) is a constant, the values of a and c increase with the increase of the Mg 2+ content of the produced samples. The mean particle size and the mean crystal grain were determined by virtue of a particle size instrument, XRD Scherrer formula and TEM method, respectively. Layered double hydroxides (LDHs) with hydrotalcite type structure containing Fe 3+, Al 3+ and Mg 2+ were prepared by means of a coprecipitation method. The products were characterized by element analysis, X ray powder diffraction and transmission electron microscopy. It was found that even if the molar ratio of n (Fe + Al) / n (Fe + Al + Mg)> 0 33, yet a pure hydrotalcite like compound (HTlc) phase was gained when n (Fe) / n (Al) / n (Al + Mg + Fe) ≤030; the Al (OH) 3 phase is in the products when n (Al) / n 0 30; and an amorphous phase born when n (Fe) / n (Al + Mg + Fe)> 0 33. These results show that there is no concentration superposition effect between Fe 3+ and Al 3+ on the crystalline state of the produced samples. In our previous work, the concentration superposition effect between Zn 2+ and Mg 2+ in the synthesis of Zn Mg Al LDHs was found. For the preparation of Fe Al Mg LDHs sa mples, the value of the lattice parameter a between 0 30-0 32 nm; and the value of the lattice parameter c between 2 30-2 47 nm, the basal spacing is in the range 0 76-0 83 nm. ratio of n (Fe) / n (Al) is a constant, the values ​​of a and c increase with the increase of the Mg 2+ content of the produced samples. The mean particle size and the mean crystal grain were determined by virtue of a particle size instrument, XRD Scherrer formula and TEM method, respectively.