Abstract: C-Mn steel was deoxidized with titanium at 1 600℃ for 15 min,then deoxidized with a MgSi alloy for different time,and at last the deoxidized samples were quenched.The effects of trace magnesium-deoxidizing time on the size distribution,composition and morphology of inclusions in Ti-deoxidized steel were systematically investigated by using an ASPEX Explorer SEM/EDS automatic analyzer system.With the prolonging of Mg-deoxidizing time,the particle number gradually decreases but the particle size increases.The size distribution of particles is in line with the normal distribution function.Since MgAl₂O₄-rich and TiO_x-rich complex inclusions aggregate and float upward,the inclusion types change from MgAl₂O₄-rich,TiO_x and MgO-rich complex inclusions to MgAl₂O₄-rich and MgO-rich complex inclusions.In addition,shortening the Mg-deoxidizing time is beneficial to a cast specimen with high number per volume unit and tiny MgAl₂O₄-rich,MgO and TiO_x-rich complex inclusions.