Abstract: 180days old Dimocarpus longana seedlings were grown in nutrition solution with three magnesium concentrations as 4 mmol·L^-1 Mg²⁺(sufficient supply),0.4 mmol·L^-1 Mg²⁺(deficient supply),and Mg free (without supply). Leaves were sampled 120 and 150 days later after treatment. With an increase in severity of Mg deficient,the chlorophyll content,PSⅡ activityes,photosynthetic rate,protein,nucleic acid (DNA,RNA),and ZRs contents declined progressively. Whereas the content of H₂O₂,the rate of O₂^-. generation as well as the content of malondialdehyde (MDA) increased. The results suggested that magnesium deficiency had significant effect on the senescence of Dimocarpus longana leaves.