Abstract: Guard cells are biochemically and anatomically the most complicated cells in the epidermal layer and are unique amongst the plant cells. Considerable progress has recently been made in studies of the specialized structure and function of guard cells and the mechanisms of stomatal movement. Various binding proteins and ion channels on the plasma membrane and tonoplast are involved in signal transduction of guard cells and regulation of stomatal movement. There are evidences that cytoskeleton plays a role in the function of guard cells.