Photosensitization of cotton and modified cottons under different conditions of exposure in presence of C.I. Vat Yellow 2 and C.I. Vat Orange 9 has been examined, and a tentative mechanism has been suggested for photosensitized degradation of cotton during irradiation by a carbon-arc source in the presence of oxygen under different conditions of humidity in the system. Comparison has been made between the behavior of chemically modified cottons during photosensitized degradation when modifications are effected prior to dye application to cotton.