Six commercial Egyptian cotton cultivars (Extra long staple) were used in this study; namely Giza 45, Giza 67, Giza 77, Giza 76, Giza 84, and Giza 87. Ten different growth regions were used also; namely; Kafr El-Sheikh, El-Beheira, Dommietta, Dakahlia, Al-Sharkeih, Al-Gharbia, El-Fayoum, El-Menya, Assuit and Sohag. The two successive seasons of this study were 1996 and 1997. Data of three replicates from each location of the six ElS Egyptian cotton cultivars were distributed in a randomized complete block design in both seasons. All tests were carried out at the Department of Botany, Faculty of Agriculture, Cairo Univ., Giza, Egypt.                 This study clear that the secondary wall thickening ranged from 14.48m in Giza 45 cv. to 18.54m for Giza 77 cv. . Also, lumen width ranged from 3.50m in Giza 45 cv. to 4.07m for Giza 70 cv. . The degree of wall thickening percent ranged from 80.45% in Giza 45 cv. to 82.45% in Giza 76 cv. . The fiber diameter (ribbon width) ranged from 18.05m for Giza 45 cv. to 22.72m for Giza 77 cv.                 Secondary wall thickening, lumen width and degree of wall thickening percent of each cultivar differed from location to location during the same season, as well as from one season to another in the same location, whereas fiber diameter (ribbon width) seemed to be little affected by environmental fluctuation.                 Giza 45 cv. recorded the finest fiber diameter (ribbon width), whereas Giza 77 has the coarest one in the ELS Egyptian cotton cultivars. This study may be help in the cultivar policy in Egypt, to determine the suitable cultivar for each area.