Nitrogen plays an important role in the growth and yield of cotton. In rigid genetical conditions, growth and development of different cotton cultivars react differently to nitrogen fertilizers. The changes in parameters of cotton fibers of different cotton cultivars that react to the application of increasing doses of nitrogen fertilizers were studied. Results show that some cultivars are more responsive to applied nitrogen than other. Apparently this is related to the differences in the absorption of nitrogen from soil resources and from the applied fertilizers. These cultivars had improved fiber quality after the application of nitrogen fertilizers in comparison to the control cultivar.