Lithium ion-substituted hexagonal strontium ferrite (Sr1−xLi2xFe12O19, where x = 0.1, 0.2, and 0.3) powders have been successfully fabricated using tartrate precursor route. The impact of Li+ content, as well as annealing temperature on the phase evolution, microstructure, and magnetic performance, was monitored by X-ray diffraction profile, scanning electron microscopy, and vibrating sample magnetometer. Single-phase hexagonal ferrite was attained at a Li+ ratio of 0.2 under a range of annealing temperatures, from 1000 to 1200 °C, for 2 h. An α-Fe2O3 impurity phase was observed at high Li+ ratios of 0.4 and 0.6 for all studied temperatures. The crystallo-aspect characteristics were altered with Li+ content and annealing temperature. The microstructure of pure hexagonal ferrite sample visualized platelet-like structure. A fine spherical with platelet shapes were displayed by increasing the Li+ ratios up to 0.4 and 0.6. Energy dispersive X-ray analysis emphasized that the Fe, Sr, O, and Li atoms spread between the plate and spherical shapes. A good saturation magnetization (Ms = 60.88 emu/g) was realized at 0.2 Li+ ratio as the result of increasing the thickness of the nanoplatelet structure.