Cell membrane- lipid peroxidation and endogenous protective enzymes activity in relation to leaf maturity of flue - cured tobacco were studied in this paper. During ripeness and senescence of tobacco leaf,contents of chlorophyll and carotenoid were continously degraded, with the degradation rate of the former more fast. After topping, SOD activities declined firstly, then went up, in lower leaves sustaining rose after ripeness of lower leaves, at the same time leaves of the other locations were reverse. POD activities and contents of Prdropped off, and MDA contents gradually rose. The key periods when the cell membrane- lipid peroxidation and anti- oxygenation reach balance were from maturation to ripeness.