Background <p>Uranium (U) contamination poses a serious threat to ecosystems. Phytoremediation offers an eco-friendly solution but is often limited by metal toxicity in plants. Arbuscular mycorrhizal fungi (AMF) can enhance plant tolerance and improve phytoremediation efficiency, while their specific interaction with polyamine (PA) metabolism under U stress remains unclear. This study investigates how AMF inoculation influences PA metabolism, antioxidant activity, and U uptake in <i>Sorghum halepense</i> (L.) Pers. ( <i>S. halepense</i>).</p> Results <p>U stress disrupted PA metabolism in <i>S. halepense</i>, leading to significant accumulation of putrescine (Put), spermidine (Spd), and spermine (Spm), with Put showing the most pronounced increase. This metabolic disturbance was accompanied by elevated levels of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), ultimately resulting in oxidative damage. Inoculation with <i>Funneliformis mosseae</i> (<i>F. mosseae</i>) enhanced the activities of key metabolic enzymes—diamine oxidase, polyamine oxidase, arginine decarboxylase, and ornithine decarboxylase—thereby promoting the conversion of Put to Spd and Spm. This shift increased the (Spd + Spm)/Put ratio by 1.99-fold and restored PA homeostasis. Consequently, AMF inoculation reduced H₂O₂ and MDA levels, raised the oxygen radical absorbance capacity (ORAC) in roots by 1.30-fold, and enhanced U immobilization, elevating root U content by 1.99-fold compared with the non-inoculated control.</p> Conclusions <p><i>F. mosseae</i> mitigated U-induced oxidative stress in <i>S. halepense</i> through the modulation of PA metabolism, thereby enhancing antioxidant capacity and contributing to increased U immobilization in roots. Accordingly, <i>F. mosseae</i> emerges as a promising symbiotic strategy for the phytoremediation of U-contaminated soils.</p> Graphical abstract <p></p>