The hypersensitive reaction is an important process in plant disease resistance. Similar to apoptosis in animals, it is programmed cell death (PCD) process in plants. Caspases (cysteine-dependent aspartate-specific proteases) play a central role in animal apoptotic pathways. No orthologous proteins of caspases have been found in plants, but a group of proteins with similar structures, termed metacaspases, have been found. In plants, some PCD processes depend on metacaspases, and others do not. We discuss researches into the structure and function of metacaspases. The biological functions of metacaspases and their roles in PCD pathways in plants remain to be explored.