The rising global prevalence of attention-deficit/hyperactivity disorder (ADHD) underscores the importance of environmental factors, particularly environmental endocrine-disrupting chemicals (EEDs), whose mechanistic links to ADHD remain unclear. The gut-brain axis, a key modulator of neurodevelopment, is susceptible to EEDs and is altered in ADHD, suggesting a potential mediating pathway. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and PROSPERO registration (CRD420251152480), we systematically searched PubMed, Web of Science, and Embase (January 2014-July 2025) for studies on EEDs, gut microbiota, and ADHD. Data from 127 included studies (observational, experimental, interventional) were narratively synthesized to evaluate the gut-brain axis as a mediator. We found 1) consistent epidemiological associations between prenatal/childhood EED exposure (e.g., phthalates, bisphenol A, pesticides) and increased ADHD risk; 2) a distinct gut microbial signature in ADHD featuring reduced alpha diversity, elevated Firmicutes/Bacteroidetes ratio, depletion of beneficial taxa (,), and impaired short-chain fatty acid (SCFA) production; 3) evidence that EED exposure induces convergent gut dysbiosis; and 4) interventional studies indicating that modulating the microbiota (via probiotics, synbiotics, fecal microbiota transplantation) can ameliorate ADHD-related behaviors. These findings support a novel mechanistic model wherein EEDs disrupt gut microbiota homeostasis, thereby contributing to ADHD pathogenesis via immune-inflammatory, microbial metabolite (e.g., SCFA), and neuroendocrine pathways along the gut-brain axis. This review synthesizes evidence positioning the gut-brain axis as a critical mediator linking EED exposure to ADHD. It proposes a unifying etiological framework and highlights the microbiome as a promising target for preventive and therapeutic strategies. Future longitudinal and intervention studies are needed to establish causality. Lactobacillus Bifidobacterium
