The reactivity of fibers of five Egyptian cotton varieties namely Giza 45, 87, 88, 89 and Giza 86 were measured before and after treatment with three swelling agents i.e NaOH (1, 5, 10 N) for 30 minutes, H2904 (10%,25%) for 15 seconds and 30 minutes for each concentration and HNO3 30 % for 30minutes. The results indicated that fiber tenacity decreased with all swelling agents used while the changes in elongation varied according to the category of cotton varie­ties. On the other hand moisture sorption %, accessibilty % and water retention% varied according to the type of swelling either intrafibrillar or interfibrillar that took place during the swelling.