The experiment of senescence in detached leaf of rice,under different treating of silicon,was performed to study the effect of silicon on concentrations of malondiadehyde(MDA)，activities of superoxide dismutase(SOD)and catalase(CAT)in senescence rice plant.Si addition,whatever before or after the separation of leaf from rice plant,significant promoted the concentration of MDA and enhanced the activities of CAT and SOD.It was concluded that Si could assist rice in delaying senescence through regulating the antioxidant defense system and Si is involved in physiological and biochemical metabolisms in plants.