Effects of milling conditions and particle size of Sr-ferrite powder on microstructure and magnetic properties of sintered Sr-ferrite have been investigated. Processes for obtaining a fine Sr-ferrite powder have direct effects upon the crystallite size and its distribution of sintered Sr-ferrite specimens. As a result of new improved processing for obtaining fine powders having a narrow particle size distribution, both Br and iHc of sintered Sr-ferrite specimens increased. Probably, these phenomena are related to the increase in the amount of crystals having magnetic single domain. To improve the particle size distribution of Sr-ferrite powder in the milling process, a new process consisting of three steps, i.e., primary milling, annealing and remilling, has been studied. In this process, annealing makes submicron particles grow into spherical particles of about 1μm. In the subsequent remilling process, residual coarse particles of more than 2μm can be milled selectively into fine particles. Consequently, the new annealing-remilling process gives Sr-ferrite powders with more uniform particle size distributions than the conventional milling process, resulting in success of fabricating high-performance sintered Sr-ferrite magnets having Br≥0.44T, iHc≥287kA/m, (BH)max≥37.4kJ/m3 or Br≥0.42T, iHc≥334kA/m, (BH)max≥34.2kJ/m3.