Microplastics (MPs) are particles smaller than 5 mm. Among their adverse effects, oxidative stress is particularly significant, as evidenced by the modulation of the antioxidant system and oxidative damage to macromolecules. Several studies indicate that aquaculture is one of the practices most susceptible to MP exposure; therefore, investigating alternatives to minimize or prevent the effects of MPs is of great importance. In this context, the use of accessible and low-cost antioxidants may help reduce the impact of MPs on farmed organisms. Chitosan is an antioxidant primarily derived from chitin, which is found in the exoskeletons of crustaceans and is considered a waste product in processing industries, despite possessing several properties, including antioxidant and immunostimulatory activity. The aim of this study was to evaluate the toxicological effects of MP exposure in Penaeus vannamei and to determine whether the inclusion of chitosan in the diet could mitigate or prevent MP-induced effects in different shrimp tissues. Over a 30-day period, shrimp were fed diets supplemented with chitosan (1 and 3 mg/kg of feed, referred to as Q1 and Q3, respectively), after which they were divided into groups and exposed to polystyrene (PS) MPs (1.0 µm in size, at a concentration of 0.5 mg/L) for seven days. At the end of the experiment, shrimp were euthanized for the collection of hepatopancreas, gills, and muscle tissues, which were then analyzed for catalase (CAT), superoxide dismutase (SOD), and glutathione S-transferase (GST) activity, reduced glutathione (GSH) levels, and lipid peroxidation (TBARS), as well as histological and accumulation assessments. Results showed that MP exposure led to increased SOD activity, indicating elevated production of superoxide anion radicals, and reduced CAT activity, thereby decreasing the capacity to manage H₂O₂. Supplementation with chitosan (Q3) reversed these effects. GSH levels were reduced in muscle and hepatopancreas following MP exposure, and supplementation with Q1 restored these levels. Lipid damage in the hepatopancreas was also observed, which was reversed by Q1. MPs caused structural damage and accumulation in various shrimp tissues. Overall, the findings demonstrate that MP exposure can induce redox imbalance in tissues and that chitosan supplementation can attenuate these effects, indicating its potential as a chemopreventive strategy in aquaculture.