Lithium-ion batteries and supercapacitors have great potential as power supplies in portable electronic devices and electric vehicles. Their performance depends greatly on the properties of electrode materials. Many attempts have been devoted to the development of new electrode materials with advanced electrochemical performances. Due to their high theoretical specific capacitance, low cost and non-toxicity, iron-based materials are considered as very promising candidates for anode materials. However, low electrical conductivity and poor cycle stability are two major problems plaguing iron-based materials. Nanomaterial design has emerged as a promising solution to these fundamental issues in LIBs and SCs. Here, we review the synthesis of iron oxide (Fe₂O₃ and Fe₃O₄) nanomaterials with various structures, including 1D (nanorods, nanowires, and nanotubes), 2D (nanosheets) and 3D (nanospheres, hollow nanostructures, flower-like structures, and nanoarrays). Nanocomposites, consisting of iron oxides and different supports (such as carbonaceous materials, other metal oxides, and polymers), are also covered in this review. Furthermore, the synthesis and structural characteristics of iron hydroxides (FeOOH) and iron sulfides (FeS₂) will also be elaborated. Finally, applications of iron-based nanomaterials in LIBs and SCs are summarized. Ultimately, we wish to provide an in-depth and reasonable understanding of how to effectively improve the electrochemical performance of iron-based anodes by selecting suitable nanostructures and optimizing their chemical compositions. Hopefully, these concepts and strategies can be extended to other nanomaterials, as a reference for future development in the areas of energy conversion, storage and environmental protection.