Objective: Number of studies evaluating oxidative stress in unipolar depression are increasing. The aim of this study was to evaluate the scores of oxidative stress in unipolar depression patients and in mixed type of unipolar depression and to compare these scores with healthy subjects in terms of dynamic thiol/disulfide balance parameters. Methods: Ninety-eight patients aged between 18 and 65 years with the diagnosis of unipolar depressive disorder diagnosed according to DSM-5 criteria and 97 age- and sex-matched 97 healthy individuals who applied to the Psychiatry Outpatient Clinic of Canakkale Onsekiz Mart University Faculty of Medicine Psychiatry Department between April 2018 and September 2018 were included in the study. Hamilton Depression Rating Scale (HAM-D) and Modified Hypomania Checklist (M-HCL) were used respectively to determine depressive symptoms, manic symptoms and the severity of the disease. Oxidative stress parameters were measured by evaluating fasting blood samples taken from all participants. Results: In the unipolar depression group, the levels of disulfide, total thiol, oxidation-reduction and oxidized thiol levels were found to be statistically significant in favor of oxidation (p<0.05). Reduced thiol levels, which are favorable for the antioxidant system, were statistically lower than the control group (p<0.05). There was no statistically significant difference between the mixed featured depression as a specifier for unipolar depression and non-mixed featured unipolar depression in thiol-disulfide balance. Discussion: The studies to be carried out longitudinally in terms of the oxidation balance, in which all depression specifiers are evaluated, will shed more light on this subject. In our study, dynamic thiol/disulfide balance parameters in favor of increased oxidation were shown to be significantly higher in the depression group than the control group. There was no significant difference between the dynamic thiol/disulfide balance parameters between the mixed depression group and the non-mixed depression group. This finding showed that the balance deteriorated in favor of oxidation in depression may not make a significant difference in terms of depression prognosis in mixed symptom depression. Longterm studies that assess all depression predictors in terms of oxidation balance will shed more light on this issue.