alpha-Crystallin is one of the major protein components in mammalian lens fiber cells. It is composed of alphaA and alphaB subunits that have structural homology to the family of mammalian small heat shock proteins. Horwitz firstly characterized native alpha-crystallin as a molecular chaperone in vitro based on its ability to prevent heat-induced aggregation of lens proteins and enzymes. Andley et al. cloned and expressed human alphaA-crystallin in Escherichia coli and confirmed its chaperone activity by suppression of thermal aggregation and singlet oxygen-induced opacification. Although alphaA-crystallin acts as a chaperone protein, there is no report showing on its ability to protect enzymes against thermal inactivation. Here, we present data showing that alphaA-crystallin can prevent thermal inactivation of CpUDG that catalyzes uracil removal from DNAs.