Background: Oxidative stress-induced damage may be involved in tardive dyskinesia (TD) development. Superoxide dismutase (SOD), the key antioxidant enzyme, was found abnormal in TD. Objective: We examined the role of oxidative stress in relation to TD and TD subtypes in schizophrenia using manganese SOD (MnSOD) as the biomarker. Methods: We recruited 152 male chronic patients with (n = 76) and without TD (n = 76) meeting Diagnostic and Statistical Manual of Mental Disorders-IV criteria for schizophrenia and 75 male control subjects. We examined the MnSOD activity for all subjects. Positive and Negative Syndrome Scale and the Abnormal Involuntary Movement Scale (AIMS) were assessed in the patients. Results: Manganese SOD activity was lower in patients with TD than non-TD (p