Mitochondria are an essential component of multicellular life and play important roles in the health of the cells and the body. Mitochondria can produce energy by oxidative phosphorylation, mediate calcium and reactive oxygen signal transduction, and regulate cell apoptosis. Recent studies indicate that mitochondria continually change their shapes and distribution by fission and fusion, which are collectively termed mitochondrial dynamics. Mitochondrial dynamics play critical roles in maintaining mitochondrial function. This review focuses on the structure and biological functions of mitochondrial fission and fusion related proteins in mammal cells.