Abstract: To investigate the roles of Ca 2 + as a signal molecule in the salicylic acid (SA)-induced triterpenoids synthesis in suspension cells of Betula platyphylla, accumulation of total triterpenes and its components in white birch suspension cells, treated by SA, Ca 2 + and the calcium channel blocker, were analyzed through UV spectrophotometry and HPLC. Also expression changes of key enzyme genes, such as FPS, SS, SE, BPW, BPY, CAS and calmodulin gene in terpene synthesis pathway of the birch cell were detected by real-time PCR. The results showed that salicylic acid can induce triterpenoid substances (total triterpene, oleanolic acid, betulin, betulinic acid) synthesis and some genes were up-regulated in birch cell suspension. Furthermore the addition of Ca 2 + would enhance the induction effect more significantly, which suggested that calcium signaling molecules in birch cells mediated the salicylic acid- induced synthesis of triterpenoid substances. In addition the results of SA combined with a variety of Ca 2 + blocker treatment showed that Ca2 + inhibition would restrain the effect of salicylic acid (SA)-induced triterpenoids synthesis. Taken together these results indicated that Ca 2 + as a signal molecule would mediate the synthesis of triterpenoids induced by SA in white birch suspension cells.