To compare the oxidative stress status between the patients with mucopolysaccharidosis who received and did not receive enzyme replacement therapy and healthy control group. Material and Methods: A retrospective study of mucopolysaccharidosis patients with analysis of the total oxidant and antioxidant capacity levels. Results: We included 29 mucopolysaccharidosis patients aged between 1-18 years and 50 healthy children. Total antioxidant capacity and total oxidant capacity parameters between this patients and healthy control group were compared. The median age of the patients who were included in the study was 9.0 years and the median age of the cases included in the control group was 8.0 years. Total antioxidant capacity, total oxidant capacity and Oxidative Stress Index (OSI) values did not differ significantly in patients receiving enzyme replacement therapy compared to patients who did not receive enzyme replacement therapy. A comparison of the oxidant and antioxidant system parameters between the patient and control groups revealed a distinct difference, with the control group exhibiting a considerably higher total antioxidant capacity than mucopolysaccharidosis patients, and the patient group showing a significantly higher total oxidant capacity and OSI. Conclusion: In this study, it was observed that the antioxidant defence system decreased in patients with mucopolysaccharidoses. It is thought that, in addition to standard treatments, the administration of antioxidant treatments and supporting nutrition in mucopolysaccharidosis patients will increase the quality of life of the patients. Regular sleep, eating healthy foods and doing regular exercise would also increase the effectiveness of these supplements.