Abstract: Chromium plays a vital role in stainless steel due to its ability to improve the corrosion resistance of the latter. However, the release of chromium from stainless steel slag (SSS) during SSS stockpiling causes detrimental environmental issues. To prevent chromium pollution, the effects of iron oxide on crystallization behavior and spatial distribution of spinel were investigated in this work. The results revealed that FeO was more conducive to the growth of spinels compared with Fe₂O₃ and Fe₃O₄. Spinels were found to be mainly distributed at the top and bottom of slag. The amount of spinel phase at the bottom decreased with the increasing FeO content, while that at the top increased. The average particle size of spinel in the slag with 18wt% FeO content was 12.8 µm. Meanwhile, no notable structural changes were observed with a further increase in FeO content. In other words, the spatial distribution of spinel changed when the content of iron oxide varied in the range of 8wt% to 18wt%. Finally, less spinel was found at the bottom of slag with a FeO content of 23wt%.