The presence of plastic in oceans is extremely worrying because they possess potential threats for marine organisms including plastic entanglement and ingestion, amongst others. Moreover microplastics (MPs) have become an emerging contaminant causing widespread concern due to its potential toxic effects associated to Persistent Organic Pollutants and other contaminants added during their manufacturing processes or sorbed to their surface once in the marine environment. However, while the number of studies documenting the ingestion of MPs by fish has increased, fewer studies have addressed the toxicological effects derived from the ingestion of MPS in long-term laboratory conditions. The aim of this study was to evaluate the physiological response of gilthead seabream (Sparus aurata) exposed to low-density polyethylene (LDPE) plastic during 90 days followed by an additional 30 days of depuration through the application of oxidative stress biomarkers in the gut. Two different treatments were applied by means of diet and three replicate tanks were randomly assigned to each treatment. Fish were exposed to a control diet without MPs and a treatment diet enriched with 10% LDPE MPs. To analyse MPs ingestion effect on the oxidative stress, inflammatory response and antioxidant and detoxification system, catalase, superoxide dismutase, glutathione S-transferase, myeloperoxidase activities, and malondialdehyde and protein carbonyl levels were determined in 81 gut samples. The results showed that compared with controls, the activities of all enzymatic biomarkers significantly increased after 90 days of exposure to enriched diet with LDPE. After the detoxification period, all biomarkers levels recovered to the initial activities, as in the time 0. As a conclusion, MPs exposure during 90 days on gilthead seabream affected the physiological response through antioxidant and detoxification enzymes activation and oxidative damage in gut, yielding novel insights into the consequences of MPs exposure of this cultivated and commercial species.