La-Zn doped M type Sr-ferrite thin films with various doping concentration were prepared by conventional rf diode sputtering. La-Zn doping reduces the grain growth rate, so that fine grains with mean grain size about 12nm were prepared with superior magnetic properties. It is found that suitable amount of La-Zn substitution may increase the Ms of the films, and modify the tempareture coefficient of coercivity, while Hc increases with increasing concentration of La-Zn.