Aging is a natural process determined by both genetic and environmental factors. Aging is accompanied by the imbalance of the function of several cellular homeostatic mechanisms, which results, among others, in the accumulation of abnormal (i.e. oxidized, cross-linked, unfolded) proteins. It has been proposed that the increased failure of homeostasis during aging is due to the impaired function of the major cellular proteolytic mechanisms mediated by the lysosome, the calpains and the proteasome. This article will address the issue of the function of these cellular proteolytic systems during aging.