The effects of atmosphere on the microstructure and magnetic properties of strontium ferrites have been investigated in this work by applying the microwaveassisted sintering process. Two different atmospheres have been selected, including micro vacuum (P = 0.025 ∼0.03 MPa) and adequate oxygen (continuously bubbled air into the oven cavity). Compared with the samples sintered in micro vacuum, the samples sintered in adequate oxygen show significant increase in magnetic properties, especially the remanence and coercivity. The optimal magnetic properties of strontium ferrite sintered at 1050 • C in adequate oxygen atmosphere are obtained as remanence (B r ), coercivity (H cj ), and maximum magnetic energy product ((BH) max ) of 422.5 mT, 386.1 kA/m, and 32.26 kJ/m 3 , respectively.