Materials used in the experiment were Azolla imbricdtcc, Azolla japonica, Azolla filiculoidcs (E.G.) and Azolla filiculoides (Ph.),and they were cultured with nutrient solution in green house for 25 days after the samples being washed by and cultured in distilled water through ioneachange resins for 48 hours, and then their contents of nutrient elements including N, P, Si, Ca, Mo, Mn, Fe, Cu, Zn, Co and B were determined. Results obtained from the experiment showed that nutrient contents in the plants of Azolla were rather high as compared with the contents of their cultural solution, which indicates Azolla has a very high absorbability of nutrients. Meanwhile, the activity of nitrogenase was also determined by acetylene reduction method. The activities of nitrogenase in the plants were in the following order:Azolla japonica>Azolla filiculoides (E. G.) >Azolla filiculoides (Ph.)>Azolla mixican >Azolla imbricata. The results by statistical analysis showed that the activity of nitrogenase (x) was very significantly positively correlated with the content of molybdenum(Y₁) (r=0.991),and it was significantly positively correlated with the content of copper (Y₂) (r=0.958) in AzoLla sampies. Under the experimental conditions the respective regression equations are as follows:Y₁=-2.71+2.43X;Y₂=0.529+0.294X.