Background: Alzheimer's Disease (AD) is the most common form of dementia seen in advanced age. It is characterized by progressive deterioration in cognitive functions. The prevalence of Alzheimer's disease increasing day by day due to the increase in the share of the elderly population in the general population due to developing health and living conditions, is limited and early diagnosis and effective treatment possibilities are very limited. From this point of view, a specific biomarker for AD is very important. As a new oxidative stress biomarker, the levels of thiol-disulfide balance, ischemia-modified albumin and seroloplazminin were evaluated. The aim of this study was to determine the serum levels of oxidative stress biomarkers in the early stages of the disease and to compare these oxidative stress markers with patients with mild cognitive impairment as a precursor form of Alzheimer's disease and to determine whether these markers develop at an earlier stage.