Oxidative stress is one of the major causes of aging considered at both the cellular and organismal levels. There is evidence that this agent may also constitute a common element connecting the aging of cells of higher organisms with a similar process occurring in eukaryotic and prokaryotic unicellulars. The aim of this paper was to present the current state of knowledge on the role of oxidative stress in aging of human somatic cells, human as a whole as well as the yeast Saccharomyces cerevisiae and bacteria Caulobacter crescentus, and Escherichia coli.