Abstract: This study was conducted to investigate the optimum synthesis and separation conditions for production of feed additive monohydrate magnesium sulfate. Monohydrate magnesium sulfate was produced using magnesia powder and sulfuric acid as raw materials by chemical synthesis method and centrifugal separation technology; the purity and flow characteristics of the product samples were tested by X ray diffraction （XRD） and Carr index method, respectively. The results showed that the optimum parameters of chemical synthesis method were as followed： sulfuric acid concentration 62%-67%, magnesia mass 45-60 g, slurry temperature 120 ℃, curing time 5 min, ripening time 25 min, magnesia powder fineness 0.15 mm; the optimum parameters of centrifugal separation technology were as followed： centrifuge speed 140 r/min, centrifugal time 1.5 h, slurry temperature was 60 ~C, under this condition, the lowest impurity content （0.8%） of SiO2 was obtained; X ray diffraction patterns indicated that the monohydrate magnesium sulfate was the single component in the product samples; the results of Carr index method proved that the flow characteristics of the product samples were good. The combined data suggest that the monohydrate magnesium sulfate produced by chemical synthesis method has the advantages of low impurity content, high purity and good flow characteristics.