The mechanical properties of single cells have been recently identified as the basis of an emerging approach in medical applications because they are closely related to the biological processes of cells and, ultimately, human health conditions. In this article, we provide a brief review of the intrinsic mechanical properties of single cells related to cancer and aging. The mechanical properties can be used as biomarkers for early cancer diagnosis because cancer cells have a lower Young's modulus, indicating higher elasticity or softness than their counterpart normal cells. The metastatic potential of cancer cells is inversely correlated with their elastic properties. Aging induces stiffness through an increased amount of cytoskeletal fiber. Changes in the mechanical properties also show potential for drug screening. Although there are several challenges to be met before clinical applications can be made, such mechanical properties of single cells may provide new approaches to human diseases.