Abstract: In the Tigris Basin, since the profit obtained from cotton is relatively higher with respect to other field plants, cotton growing has been preferred more and continued without crop rotation. Due to lack of crop rotation, Verticillium wilt of cotton (Verticillium dahliae Kleb.) becomes a significant problem. In this study, through inhibiting or declining Verticillium wilt of cotton, we aimed to increase crop yield by Paclobutrazol (PBZ), which is a growth retardant. The dose and time of application of PBZ were determined at Nazilli 87 in 1998 and Sur-Grow SG 501 cotton varieties in 1999. In the research, it was determined that the retardant was effective in declining the disease. It was also established that, in case of early application and dose increase, the inhibitor was more effective in declining the disease, however leading to yield lose due to excessive stocky and dwarfing. It was considered to arrange more plants per unit area in order to benefit from dwarfing of the retardant mentioned and therefore, the yield was increased about 48% at Maras 92 variety in 2000, through its 0.05 g m-2 of application dose after the second irrigation without decreasing density 20 plant m-2, which is a significant for cotton labour work. In conclusion, the application of Paclobutrazol at a dose of 0.05 g m-2 was considered suitable after the second irrigation without decreasing the density (through more plants per unit area), when the plant height reaches 40-50 cm.