Nanosize LiNi x Fe1−x PO4 solid solution and LiNi x Fe1−x PO4/C nanocomposites were prepared via a solid state reaction method under argon atmosphere. A single phase olivine-type structure with Pnma space group was determined by X-ray diffraction. Crystallite sizes were found to be around 50nm. A linear relationship was observed between lattice parameters and chemical composition which follows Vegard's law. Synthesized materials displayed electronic conductivity similar to previous reported values of LiFePO4. Carbon coating further increased the overall conductivity of nanocomposites to the order of 10−3 S/cm. Chemical delithiation via NO2BF4 oxidant extracted more than 95% of lithium from the solid solution material accompanied by a decrease in lattice parameters.