<p>Bisphenol A (BPA) is a widespread contaminant of increasing concern because of its persistence in soils and its ability to interfere with hormonal regulation. Although its harmful effects on plant roots are relatively well described, its impact on arbuscular mycorrhizal fungi (AMF) remains poorly understood. In this study, we examined how different BPA concentrations (0, 10, 20, 50, and 100 mg L^− 1) affect transformed carrot (<i>Daucus carota</i> L.) roots, grown either alone or in association with <i>Rhizophagus irregularis</i>. Root growth stopped completely at the highest concentrations (≥ 50 mg L^− 1), while intermediate levels (10–20 mg L^− 1) reduced root area, length, and branching. At 10 mg L^− 1, roots still developed similarly to controls, but fungal growth outside the roots and spore formation were already reduced. At a concentration of 20 mg L^− 1, the fungus successfully colonized the internal root despite the absence of external hyphae and a marked inhibition of root growth. In both mycorrhizal and non-mycorrhizal roots, oxidative stress increased at 10–20 mg L^− 1, suggesting that reactive oxygen species (ROS) play a central role in mediating the toxic effects of BPA and possibly in signaling stress responses. Altogether, these results show that BPA disrupts the balance of the plant–fungus relationship, limiting fungal development and altering root physiology, even when colonization persists. Considering the ecological role of AMF, our findings underline the need to include these symbiotic fungi in environmental risk assessments and in strategies aimed at restoring soils contaminated with emerging pollutants. Given the scarcity of previous research, our study provides the first direct assessment of this topic, suggesting that our results may help shape future research in this emerging field.</p>