The magnetizing roasting and magnetic separation without addition of reductant were used to treat all-size siderite iron ore from China for recovery of iron concentrate. The results showed that the final iron concentrate containing 63.15% total Fe content with the iron recovery rate of 92.52% was obtained under the conditions of roasting of siderite ore at 800℃ for 15 min without addition of reductant, and separation of roasted ore by grinding up to the particle sizes of below 0.074 mm with 90% at 0.10 T magnetic field intensity. The elements of Mn, Mg and part of Ca existed in the form of isomorphism with Fe in the iron concentrate.