Abstract: Three sugarcane C.V. ROC22, GT17 and ROC10 were soaked with ethephon in three concentrations 0mg/L, 100mg/L, 200mg/L for 10 minutes before planting in sand, and water stress was applied at the young shoot stage (four to five leaves). The effects of ethephon seed soaking on protein and nucleic acid in sugarcane leaves under water stress were investigated. The results were as follows: The ethephon seed soaking treatments showed much higher protein content, nucleic acid content and lower activity of protcase under the water stress and after re-watering. The ethephon seed soaking treatments increased much higher the ratio RNA to DNA in leaves of ROC22 and GT17 under water stress, and showed promoting effects on the ratio RNA to DNA in leaves of the three sugarcane varieties. So the tillering was increased.