Until today there are many works have been done to improve this white gold crop. This work is an attempt to study cotton fibers using X-ray technique, and I think as it looks easy but it is very useful to understand the the desired mechanical properties of cotton fiber through the crystalline structure of these fibers. In this work, I have studied the effect of crystalline structure defects on the elastic modulus of cotton fibers. As will as, I have selected different species of cotton fibers which cultivated in India and Yemen. I hope this research work will be first step to develop the cultivation of this crop in my country (Yemen).