Abstract: After submerging tobacco seeds with CaCl2 solution, we studied the effect of Ca2+ on activities of certain enzymes in tobacco seedlings. It was shown that submerging tobacco seeds with CaCl2 solution increased the content of combinative calcium in tobacco seedlings and the protective enzyme activity, and reduced the permeability of cell membrane and the content of MDA. Under the low temperature stress, the reduction of SOD, POD and CAT activities in the tobacco seedlings treated with Ca2+ was lower than that of control seedlings . The relative electric conductivity of cells in tobacco seedling treated with Ca2+ also reduced. The recovery of cell membrane permeability of tobacco seedlings treated with Ca2+ was faster than that of control seedlings after seedling growth re sumed. CPZ, the special inhibitor of CaM, could partly restrain the function of Ca2+ in increasing the activities of SOD, CAT and POD.