Abstract: Calcium is the second messenger involved in multiple signal transduction pathways. Distribution of ［Ca2+］cyt in guard cell and changes of ［Ca2+］cyt in duced by exogeneous stimuli can be showed by using Ca2+fluorescent imaging technique, and the mechanisms of Ca2+release from intracellular and extracell ular Ca2+pools are partially revealed. The Arabidopsis mutants in some given sites show that those components also involved in Ca2+signal transduction pathway and provide molecular evidences for Ca2+signaling in guard cell. Other essential processes are phosphorylation and dephosphorylation which are downstream of [Ca2+］cytelevation.