Background and Aim: The increasing accumulation of micro- and nanoplastics in the environment and their subsequent entry into the food chain have raised serious concerns regarding their health impacts, particularly on the gastrointestinal tract. This review aims to analyze the molecular mechanisms of intestinal injury induced by exposure to micro- and nanoplastics, focusing on intestinal barrier dysfunction, oxidative stress, and the inflammatory response. Materials and Methods: This study was conducted as a narrative review based on the analysis of 58 selected articles from the PubMed, Scopus, and Web of Science scientific databases. The literature search was performed using relevant keywords covering the period from 2014 to 2026. Articles based on animal models (zebrafish, mice), cell cultures (Caco-2), and human studies that investigated the consequences of oral exposure to plastic particles on intestinal health were selected, and their molecular data were extracted. Results: Exposure to micro- and nanoplastics (particularly polystyrene and polypropylene) leads to particle accumulation in the intestine, induction of oxidative stress, and production of reactive oxygen species (ROS). ROS, in turn, disrupts intestinal barrier integrity by reducing the expression of tight junction proteins (e.g., ZO-1, occludin) and activating key inflammatory pathways such as NLRP3/caspase-1 and TLR4/NF-κB. These processes are associated with increased intestinal permeability, local and systemic inflammation, and the induction of apoptosis and pyroptosis in epithelial cells. Conclusion: Current evidence indicates that micro- and nanoplastics can critically compromise gut barrier health and predispose individuals to inflammatory and metabolic disorders through the induction of a cascade involving oxidative stress, inflammation, and cell death. Long-term studies employing environmentally relevant concentrations and investigating the combined effects of other pollutants are essential for a more accurate assessment of health risks.