The transition metal iron (Fe) has attracted particular interest in pursuit of low-cost oxygen reduction reaction (ORR) electrocatalysts. Carbon-supported iron oxides and oxyhydroxides have demonstrated promising ORR catalytic activities, but there is limited knowledge regarding the influence of iron species types and their crystalline phases on their ORR activities. In this paper we synthesized four iron/graphene composites with iron oxides (α-Fe₂O₃, Fe₃O₄) and oxyhydroxides (α-FeOOH, and α/γ-FeOOH) supported on graphene oxide (GO), and systematically investigated their ORR behaviors. It is found that decorating GO with iron oxides and oxyhydroxides can dramatically improve the ORR activity of pristine GO in alkaline solution in terms of onset potential and current density, and the α-Fe₂O₃/GO exhibits the highest ORR activity among all four composite materials investigated. This study unveils diverse ORR behaviors on GO-supported iron species, and explores the benchmark of their catalytic performances, and thus provides useful insights into the Fe-enabled high ORR activity for developing efficient transition metal-based ORR electrocatalysts.