Abstract: The result of investigation indicated that tolarance of Hybrid Azolla to salt was the best,followed by A.filiculoides and A.microphylla among three Azolla treated with different salt concentrations) during low salt concentration,Azolla were grown beneficially.The SOD activity rose higher with the increasing intensity of salt stress,but it started to reduce in certain salt concentrations (A.filiculodes and Hybrid Azolla in 0.6% NaCl,A.microphylla in 0.4% NaCl).The SOD gel electrophoresis showed the same results between SOD activity and straining intensity of enzyme bands.The ultrastructural changes of mesophyll cells showed that damage of membrance systems might be as s result of lipid reoxidation.It is suggested that SOD activity might be as an index of NaCl-resistance breeding.