Abstract: In the course of maturation of cotton bolls spraying with ethrel (200–2000 ppm) on cotton plant has a marked hastening effect on ripening. The bolls of treated plants cease to grow, rapidly mature and dehisce to emit fibers. For the fully grown bolls (middle and lower fruiting branches of cotton plants) both the boll weight and fiber quality are slightly improved, while for the rapidly growing bolls (upper fruiting branches.), the boll weight decreases. At the same time the leaves, flower buds and young bolls (less than 10 days old) shed. The higher the spraying concentration the more rapid and stronger the accelerating effect. At the time of spraying, the presence of too many young bolls and the use of an excess concentration, will effect both the yield and quality of cotton. Based upon the experimental results, a rational application of ethrel for the purpose of hastening the ripening of the cotton bolls has been proposed.