Multi-component white cast iron was developed for rolling mill rolls and is spreading widely. The morphology and alloy concentration of crystallized carbides were investigated by SEM, TEM and EDS analyses using three irons with typical chemical composition of Fe-2%C-5%Cr-5%V-Mo-W (mass%) system, and the influence of Mo and W on these irons was studied. The reaction of M₂C + γ-Fe → M₆C + MC + M₇C₃, which occurs by heat treatment, could be suppressed by increasing Mo content. It was found that there exists a linear relation between alloy content in each carbide and Mo ratio Mo/(Mo + W) of molten metal. In high W material, however, W contents of crystallized MC, M₂C and transformed M₆C crbides were saturated values.