Abstract: The oleaster leaf-spot caused by Septoria argyraea Sacc.is a discase of oleaster tree which is an important nitrogen fixation woodly plant.Some nodules exist on its root,which can fix the nitrogen from air.As more the leaf spots produced the damages are resulted.The number of nodules appeared to be correlated to the serious grave of the disease.Experiment shows that the damages produced by the disease are: Lowing the number of the nodules. Weakening the activity of N-fixation of the nodules. Decreasing the growth race as well as the Nitrogen content of the plant. Because of the disease,infected plant are 3—6 times less than normal plant in dry weight,3—16 times in number of nodules,21—100 times in centent of the nitrogen fixation.