Granzyme is an effector molecule of activated cytotoxic T cells and natural killer cells. It mainly mediates cell apoptosis. Its function could be explained by its molecular characteristics to some extent. Its cytotoxic effect is related to some other factors contributing to apoptosis induction. It deserves studying if perforin mediates entrance of granzyme into cells. As potential substrates of granzyme caspases and their substrates have been paid much attention to.