The effects of air pollutants on textiles were investigated. The effects of NO*l2*s and SO*l2*s gas, the main components of air pollutants, and that of humidity on the physical properties of cotton and silk threads and also on the color fading behavior of natural dyes were examined. Both the strength and elongation of the threads were affected more strongly by NO*l2*s than by SO*l2* s gas. The strength of cotton began to decrease at 684ppm.h of NO*l2*s dose and even became 55per thousand of the untreated at 1140ppm.h, whereas change did no appear until 1140ppm.h of NO*l2*s dose for silk. The change of strength in both threads by SO*l2*s gas did not appear until 1348ppm.h. The change in elongation, however, appeared from a lower dosage for both NO*l2*s and SO*l2*s. The fading of natural dyes tested were greater with NO*l2*s than with SO*l2*s gas, showing greater change on cotton than silk. With NO*l2*s gas exposure, fading was accelerated by high humidity. The above results indicate that the presence of both NO*l2*s and SO*l2*s must be taken into account for the conservation of cultural properties made of textiles.