Abstract: To understand the refinement mechanisms of inclusions in steel,the morphology,size,composition and number of inclusions in low C-Mn steel were characterized by scanning electron microscopy and energy dispersive spectroscopy. The predominance area diagram of deoxidation products was calculated. Some factors which influence the growth of inclusions was discussed. It is found that inclusions in Ti-Mg deoxidized steel are composed of MgO-Al₂O₃-TiO_x,then MnS encapsulated and precipitated on them,isolated Al₂O₃ and TiO_xdo not appear in the steel. The inclusions' morphology is spherical,the average size is about 1.0 μm,and the number is more than 1000 mm^-2. Few MgO-Al₂O₃ and MgO inclusions exist in the steel with high Mg content. Therefore,high Mg content in molten steel is harmful to the control of sphericizing,and it should be restricted to below 50 × 10^-6. Magnesium has strong deoxidation ability,and the deoxidation products have the characteristics of small critical radius,large number of nucleation,and the formation of Al-Ti-Mg-O complex inclusions,which both control the supersaturation of oxygen and the growth of inclusions in the steel.