Background. Demographic transition is indication of population growth rates which impacted by global environmental changes and development of modern science. Last years, number of elderly people dramatically increasing in the world and this increases also showed up in Mongolia. Therefore, investigating the ageing process, risk factors for ageing and age related changes of the human body is important for diagnosing and decreasing age-related disease, improving the quality of life in elderly and healthy ageing. We aimed to investigate age related changes of antioxidant and prooxidant status among healthy Mongolian adults.Materials and Methods. 384 healthy subjects participated in this research. We measured serum level of antioxidant and prooxidant parameters in all subjects at the Functional diagnostic laboratory and Immunology laboratory of the Health Sciences University of Mongolia.Results. Serum level of malondialdehyde (MDA) that is parameter of prooxidant activity was lower in the 21-30 age groups and highest in upper 70 age groups. There was a significantly positive correlation between age and serum MDA level (r=0.665, p 0.01). Serum antioxidant parameters such as superoxide dismutase (SOD, r=-0.357, p 0.01), glutathione (GSH, r=-0.201, p 0.01) and total antioxidant activity (TAC, r=-0.256, p 0.01) has a negative correlation with age. But glutathione peroxidase (GPx, r=0.635, p 0.01) was significantly increased with age. That means the antioxidant activity is decreasing with the ageing process. Regression analyses showed that MDA, GPx, SOD, GSH, and TAC were significantly related with the ageing process.Conclusion. We concluded that the antioxidant activity is decreasing and oxidation process is increasing with age and oxidative stress is higher in healthy Mongolian adults. Furthermore, the serum lipid level is increasing from age 40and it can be the reason for arterial wall thickness.