This study is to detect the synthetic condition for the formation of Sr-Ferrite(SrFe12O19) by hydrothermally reaction. Mixed suspension of SrCl26H2O and FeCl3 6H2O were fixed on pH and were subjected to autoclavings at various temperature(150∼300$^{circ}C$), reaction time(2hrs.∼48hrs.). The Sr-Ferrite powders were synthesized at 150$^{circ}C$ for 36hrs, 200$^{circ}C$ for 4hrs and 250$^{circ}C$ for 2hrs. Synthesized powders were increased particle sizes at longer reaction time and higher reaction temperature. It has hexagonal ferrite M-type structure and has high purity of SrO.5.6 Fe2O3 composition.