Abstract: The nodualization effect of cast iron treated by rare earth alloys was compared with ones treated by magnesium alloys. As the ratio of residual rare earth content to residual Mg in cast iron is 3:1, the same nodu-alization effect will be obtained. A proper composition for rare earth sphe-ro idual graphite cast iron is as C ≤ 4.0%, E.C ≥ 5.0%, S<0.01%, RE ≥ 0.1%. and there is no defference in chilling tendency between RE-SG and Mg-SG.By means of injecting rare earth powder, the speed of reaction of desulphurization is higher, and the limit of dcsulphurization is close to the thermodynamic equilibrium. If the amount of RE to be added into liquid iron is properly controlled, desulphurization,nodualization and inoculation can be finished at a time