An innovative iron supplement crucial for treating iron-deficiency anemia was developed in this study. Polysaccharide was extracted from Eucommia ulmoides leaves using a microwave-assisted hot water method, and subsequently, the polysaccharide–iron complex was synthesized through co-thermal synthesis with FeCl₃. The physicochemical properties, structure, and thermal stability of the complex were analyzed using FE-SEM, SEC-MALLS, FT-IR, XRD, and DSC techniques. Furthermore, the antioxidant activity of the polysaccharide–iron complex was evaluated through an experiment in vitro. The results revealed that the polysaccharide–iron complex had an iron content of 6.1% and an average particle size of 860.4 nm. The microstructure analysis indicated that the polysaccharide–iron complex possessed a flaky morphology with smooth and compact surfaces. Moreover, the formation of the Fe³⁺ complex did not alter the structural framework of the polysaccharide; instead, it enhanced the polysaccharide’s thermal stability. Compared to traditional iron supplements, the E. ulmoides-derived polysaccharide–iron complex demonstrated significant antioxidant activity. Therefore, this novel compound exhibits significant potential as a viable iron supplement.