Abstract: The growth of sorghum seedings, ion contents, relative plasmalemma permeability and gas exchange of the leaves under iso-osmotic NaC1 and KC1 stress were studied. The results indicate that under the stress of low concentrations of NaCI and KC1 for 7 days, the growth of the seedings, water content and relative plasmalemma permeability of the leaves were not significantly affected compared to control plants. But the net phytosynthetic rate, transpiration rate and stomatal conductance were markedly decreased and the intercellular CO2 concentration was markedly increased. Correspondingly, the Na+ content in the leaves increased many times under NaC1 stress, but K+ and Ca2+ contents were not obviously altered. The K+ content significantly increased and the Ca2+ content significantly decreased under KCl stress, but the Na+ content was not affected. With the increase of NaCl or KC1 concentration, the growth of the seedings and the leaf water content markedly decreased, but relative plasmalemma permeability and intercellualar CO2 concentration significantly increased, and the net photosynthetic rate, transpiration rate and stomatal conductance further decreased, The Na + content in the leaves further increased, and the K+ and Ca2+ contents in the leaves decreased with the increase of NaC1 concentration. Similarly, the K+ content in the leaves further increased, and the Na+ and Ca2+ contents further decreased with the increase of KCl concentration. KCl had much more detrimental effects on the growth, plasmalemma permeability, Ca2+ metabolism and photosynthetic gas exchange of the sorghum seedings than iso-osmotic NaCl.