Fiber absorbents are among the most economical materials for uranium extraction from seawater. Marine organisms are prone to fouling while being deployed in the sea, severely impairing the adsorption properties of the fiber. In this study, a novel antimicrobial adsorbent (UHMWPE-g-GEAO) was prepared by grafting guanidino and amidoxime groups onto ultra-high molecular weight polyethylene (UHMWPE) using radiation-induced graft polymerization technique. The guanidino groups endowed the fiber with excellent resistance to biofouling, enabling it to kill 99.9% of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). UHMWPE-g-GEAO fibers exhibited a fast uranium adsorption rate and high adsorption capacity, reaching 156.00 mg/g in aqueous solution and 1.39 mg/g in real seawater within 14 days. Additionally, the adsorbent exhibited superior reusability, preserving more than 94.5% of its adsorption efficiency and 96.2% of its desorption efficiency after five adsorption-desorption cycles. In this study, a reusable UHMWPE antimicrobial adsorbent fiber with promising potential for uranium extraction from seawater was developed.