Aging is accompanied by the changes in the cells that decrease their capacity to respond to various forms of stress. Cells are known to respond to stresses through expression of stress-response proteins, heat-shock proteins composed of molecular chaperones. Recent studies suggest that chaperone level and stress-induced chaperone expression could decrease with aging. The aim of the present study is to identify chaperones that show a significant change in protein expression with aging. We used an in vitro aging model system of human diploid fibroblasts (HDF). Proteome analysis of HDF showed that endoplasmic reticulum (ER) chaperone, calnexin, significantly decreased with aging. Oxidative stress-induced expression of calnexin also attenuated in old HDF compared to young cells. These findings suggest calnexin decreases with aging and might contribute to a cytoprotection in a variety of human age-related diseases.