Abstract: A pot experiment was conducted to investigate the effect of decapitation (a conventional technique in cotton cultivation in Xinjiang) on the premature senility and contents of phytohormone, carbonhydrate and chlorophyll in the functional leaves of cotton plant under low (150 mg·kg_-1) and high (500 mg·kg_-1) nitrogen application. Compared with non-decapitated plants under low nitrogen application, CTK and soluble protein content decreases while ABA and MDA content increases in decapitated plants. Both CTK and soluble protein content increases when smeared with NAA after decapitation in relation to decapitation only or non-decapitation treatments. ABA content in plants smeared with NAA after decapitation is lower than in decapitation only, but is higher than in non-decapitation treatment. ABA/CTK ratio for cotton plant with decapitation treatment is higher than in non-decapitation or post-decapitation NAA-smearing treatments. Decapitation increases plant MDA content while MDA decreases in post-decapitation NAA-smearing treatment, compared with non-decapitation treatment. Under higher N supply, ABA content under decapitation or post-decapitation NAA-smearing treatment is higher than under non-decapitation treatment. Chlorophyll content in leaves under low N supply is higher than under high nitrogen supply. Accumulation of ABA under high nitrogen supply indicates that high N might inhibit plant growth. The increase in ABA and MDA content and in ABA/CTK ratio under decapitation with low N supply suggests that decapitation enhances premature senility of cotton plants. Post-decapitation NAA smearing, on the other hand, may delay premature senility.