Abstract: During maturing of Tobacco leaf, the activities of superoxide dismutase (SOD) and catalase (CAT) decreased and the level of lipid peroxidation and the permeability of cell membrane increased at various rates in different stages of development. From immaturity to proper maturity stage, those changes in activities were quite slow. Thereafter, those changes were accelerated markedly, the results indicated proper maturity stage was key period for tobacco leaf turning to senescent, the maturity and senscence of tobacco leaf were related to the metablic disorder of active oxygen. In addition, the contents of fatty acids in tobacco leaf changed obviously during maturing. With the development of leaf, lauric acid increased, palmitoleic acid, oleic acid and eicosenoic acid decreased, but many fatty acids, such as tridecanoic acid, myristic acid, palmitic acid, stearic acid and linoleic acid, reached their maximum contents at proper maturity stage.