In this paper, the nanopowders of Li(Li0.21Mn0.54Ni0.125Co0.125-x)FexO2 (x=0% , 0.01% ,0.025%, 0.05%, 0.075 and 0.10% ) were prepared by sol-gel method, and the thermal, structural and chemical properties of the samples were investigated. These properties of samples characterized by thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray diffraction (XRD), field-scattering microscopy (FESEM), X-ray energy spectroscopy (EDS), Transmission electron microscopy (TEM) and infrared spectroscopy (FTIR). The results of characterization were investigation. TG/DTA measurements showed weight loss in these nanopowders The XRD results reveled crystalline structures for pure and impure nanoparticles. The layerd structure remains unchanged to % 0.05 Fe but From the percentage of 0.075% to above, the additional peak, which are related to the formation of the secondary phase of LiMn2O4, have been observed in the structure, which confirms the cubic structure in addition to the hexagonal. The FESEM images for pure and impure samples have shown to be agglomerated with relatively spherical and hexagonal particles of<130 nm. Image tools software was used for illustrating the distribution of particle size for pure and 0.01% Fe of impurity of nanopowders. The results of TEM revealed that with the presence of iron, the size of the particles is larger than pure nanoparticles and the range of 50-150 nm. In infrared spectroscopy (FTIR), the connection bonds and chemical elements used in these nanopowders have been investigated.