Abstract: A magnesite ore treated in a mineral processing plant in Liaoning province belongs to low-grade ore bearing high silicon and calcium, and the reverse-direct flotation flowsheet was adopted, but there was in a state of shutdown due to the poor technical and economic indexes caused by the problems existing in the original flowsheet such as poor liquidity and selectivity of collector froth, severe entrainment of useful mineral, unstable flowsheet operation and the difficulty in implementation of closed-circuit production in the reverse flotation stage, poor effect of calcium removal in the direct flotation stage, big loss and low recovery of magnesite (only 35% of MgO recovery), etc. Based on the problems existing in the original flowsheet, it was proposed in this paper to treat the ore by the process of iso-flotability reverse-direct flotation, namely, iso-flotability reverse flotation with water glass as regulator and novel anionic collector BK-428 under condition of weak acidic pulp (pH 6.0) was adopted to remove silicate and dolomite, and direct flotation by sodium hexametaphosphate as regulator and cationic collector BK410B under condition of weak alkali pulp (pH 9.0) was used to further remove dolomite and silicate, and it could realize the quality improvement and impurities reduction of low-grade magnesite ore. By this new process, based on the systematic laboratory tests and continuous pilot tests, the industrial tests were carried out and the magnesite concentrate with a MgO grade of 47.14% and a recovery rate of 76.02% was obtained from the low grade magnesite ore with MgO 42.94%, while SiO₂ and CaO content in concentrate decreased from 4.14% and 2.91% to 0.28% and 0.53% respectively.