Abstract: The effect of different rotation systems on the fiber quality of cotton under the irrigated conditions of Diyarbakır, was studied. Cotton is cultivated for the first year and main winter product+second product are cultivated in the second year, that is, three products are cultivated in two years, 12 rotation systems consisting of cotton–cotton, cotton–wheat+maize, cotton–wheat+rice, cotton–wheat+sunflower, cotton–wheat+soyabean,cotton–barley+maize, cotton–barley+silage maize, cotton–lentil+maize, cotton–lentil+silage sorghum x vetch hybrid, cotton–chickpea+maize, cotton–chickpea+soyabean and cotton–common vetch x barley mixture+maize were analyzed. It was identified that the length of fiber (fibrograph 2.5%), rate of oil in cotton seed and first hand % are significantly affected by the rotation systems whereas cotton–gin output, 100 seed weight, fiber strength and thickness of fiber are not statistically affected.