This experiments were conducted in Nanjing (118°50’, 32°02’) and Xuzhou (117°11’, 34°15’), Jiangsu Province, China, to study the response of fiber quality to the N concentration of the leaf subtending boll in cotton (Gossypium hirsutum L.). Results suggested that the N dilution curve of the leaf subtending boll can accurately indicate the stage-specific plant N status for fiber development. Fiber strength is likely to be the most variable fiber quality index responding to the leaf N variation which is different in cultivars. Fiber length was the most stable index among strength, length, micronaire, and elongation. There existed an optimum leaf N concentration for fiber strength development in each stage. The optimum leaf N regression curve was very close to the N dilution curve in the middle positional fruiting branches under the 240 kg N ha-1 soil N application rate. This experiments were conducted in Nanjing (118 ° 50 ’, 32 ° 02’) and Xuzhou (117 ° 11 ’, 34 ° 15’), Jiangsu Province, China, to study the response of fiber quality to the N concentration of the leaf Substituted boll in cotton (Gossypium hirsutum L.). Results suggest that the N dilution curve of the leaf subtending boll can accurate indicate the stage-specific plant N status for fiber development. Fiber strength is likely to be the most variable fiber quality index responding to the leaf N variation which is different in cultivars. Fiber length was the most stable index among strength, length, micronaire, and elongation. There was an optimum leaf N concentration for fiber strength development in each stage. very close to the N dilution curve in the middle positional fruiting branches under the 240 kg N ha-1 soil N application rate.